Instigator / Pro

Rationalism (pro) vs Empiricism (con)


The debate is finished. The distribution of the voting points and the winner are presented below.

Winner & statistics
Better arguments
Better sources
Better legibility
Better conduct

After 2 votes and with the same amount of points on both sides...

It's a tie!
Publication date
Last updated date
Number of rounds
Time for argument
Three days
Max argument characters
Voting period
One month
Point system
Multiple criterions
Voting system
Contender / Con

Round 1: Acceptance

Round 2: Opening Arguments

Round 3: Rebuttals / Opening Arguments

Round 4: Rebuttals

Round 5: Closing

Empiricism: Sense Experience is the only way to attain knowledge and determine if claims are true. All knowledge comes from the senses.

Rationalism: All Knowledge primarily comes from Reason rather than sense experience.

Round 1
BOP is shared. Apologies on the debate layout, I thought this website was similar to DDO where an entire round had to be used for acceptance.
No worries. I will follow the presented debate structure. I accept the debate.
Round 2
Thank you con for accepting the debate and Good luck!

Argument 1: Empiricism is self-defeating.

Empiricism, as defined in the description, is the claim that “all Knowledge comes from the senses and that sense experience is the only way to determine if a claim is true”. The problem that rationalists have pointed out is that the claim that “all knowledge comes from the senses” is not itself knowledge that comes from the senses. There is simply no experiment or place where we can observe such a claim. Since empiricism makes a claim that fails by its own criteria, it is a self-refuting proposition similar to “There are no sentences that are more than 3 words”.

Argument 2: Empiricism undermines its own evidential foundations

Empiricism, as an ideology, lies on a number of claims such as “the senses are reliable” and “the external world is real”. If either of these assumptions is false, empiricism clearly falls apart; since if the external world is not real or instead say, some hallucination or extended dream by a Cartesian demon, then there is no reality to sense or experience any information from. If the senses are not reliable, then no trustworthy knowledge comes from the senses since they are relaying false information. The problem is that these claims rest on philosophical foundations that can only be justified on the basis of reason. The problem is that a claim like “the senses are reliable” is not knowledge that comes to us through the senses because it similarly cannot be observed anywhere or determined from any experiment. The bigger problem is that such a claim can not possibly be justified on the basis of sensory experience. Since any empirical argument for the reliability of the senses will have to assume that the information being relayed from the senses is reliable in order to infer conclusions from. But whether the senses are giving us true information is the very thing in question.

So any empirical argument for the reliability of the senses will assume that the senses are reliable and are relaying correct information and will, therefore, be a circular argument - on the level of the Bible is true because it says so. So empiricism not only fails to justify its own assumptions and foundations but directly undermines them. As a result, Empiricism forces itself into relying on unjustified assumptions that could not in principle be vindicated through empiricism. Since any claim is true on the basis of its justification, then no empirical knowledge is justified or true on the basis of ultimately resting on unjustified foundations. The justification for empirical knowledge relies on the validity of the senses, which itself cannot be established empirically but only through reason, so ultimately even empirical knowledge rests on reason.  

Argument 3: Rationalism as a framework

The rationalists identify 2 axioms that undergird their epistemological foundations. The first being the notorious “I think therefore I am” and the second being the reliability of reason. The mind or consciousness is simply our ability to think or have thoughts. The fact that we can think about the possibility of the mind being an illusion presupposes the ability to think and therefore presupposes the mind. So the possibility of even doubting your existence or the existence of your mind is proof that the mind exists. Moreover, we must affirm that the rational faculty of the mind is capable of valid reasoning for if they were unreliable and utterly incapable of making correct conclusions then their belief that “the rational faculty of the mind is unreliable” would itself be unreliable or incorrect since it is the result of an unreliable rational faculty - making such a view incoherent. So we can be certain about the existence of the mind and the reliability of its rational faculty. These are already two truths that we know apart from experience and that would disqualify empiricism.

From there, we can derive some a priori knowledge from reason alone such as the laws of logic, the laws of mathematics, causal principles and so on. Take one example, the axiom “something cannot come from nothing” that forms the basis for almost all causal principles. The justification for that axiom would be that nothing is the lack of anything and therefore would also lack causal powers. Since it has no ability to produce any effect, then the effect must come from some pre-existing reality and that is what we mean by a cause. This is another truth that we can prove on the basis of reason alone sans any empirical practice and would refute the claim that “all knowledge comes from the senses”.

What is Knowledge?

The branch of philosophy that deals with knowledge is known as epistemology. It defines knowledge, simply, as a "justified true belief." What to each of these mean? 

Belief is easy: it is simply what you accept as true.

True is a bit harder. While it may seem obvious, describing exactly what makes something "true" can be elusive. To distinguish true belief from a false belief, we most necessarily posit the existence of some objective realty that is external from the source of our beliefs. Empiricism points to the physical universe, while rationalism depends on a logical framework. Something is true, then, if the belief is consist with, and does not contradict, this external, objective reality.

Justification is even harder. Justification is the primary point of debate within epistemology about what constitutes knowledge. As hard at it is to define, without justification, beliefs which just coincidentally happen to be true would count as knowledge. Since this is not permissible, the requirement of justification is introduced, even though there is no universal consensus about the minimum justification necessary to define what is "knowledge." While the exact nature of justification is in dispute, the two main camps within epistemology are evidentialism (there exists evidence in support of a belief) and reliabilism (the belief originates from reliable cognitive processes).

Empirical Justification

Empiricism provides a solid basis for objective truth in the existence of a physical reality in which beliefs can be compared. A belief is true if and only if it corresponds to the state of reality. For example, the belief "it is raining" is true only if it is, in fact, raining. However, it does not offer much in the way of justification. PRO states the oft repeated criticism of empiricism that our senses are not reliable. Or, more accurately stated, they are not infallible. Does justification require perfection? Perhaps, but if so, neither empiricism or rationalism can provide it: knowledge would simply be unattainable.

Within an empirical framework, evidence abounds. Through our senses, we experience the real world and discover truths about it. The limitations of our senses are mitigated through repeated observations and comparison of observations among independent viewers. Over time, with enough independent observations, we construct a body of knowledge about the world.

Rational Justification

The lack of perfection of our senses is enough for rationalists to discard them as unworthy to attain knowledge. In fact, some might even question the existence of a physical world at all! Lacking this, what is "true" in a rational point of view? What is "justified?" Within rationalism, truth depends on the logical framework one is operating in. What is a logical framework? It is a set of axioms and rules of inference. From these axioms, we can derive additional theorems. So long as the do not result in contradiction, a theorem is true. Thus a belief is true if it exists as a theorem within our logical framework. Justification comes from how well the thought process that resulted in the belief aligns with the permitted axioms and rules of inference defined by the logical framework.

Seems simple enough. But where do the axioms and rules of inference come from? Easy: we made them up. There is no universal set of axioms or rules of inference a logical framework must have or must exclude. Indeed, many wide and varied logical frameworks have been devised simply by deciding to try different combinations of axioms or rules of inference. There are no rules for the rules, as it were. And if there were, those rules would simply be a set of axioms or rules that would have to be posited and accepted. In the end, the axioms and rules are simply what one chooses them to be. And since the theorems of a logical framework are strictly derived from these axioms and rules, all truths within that framework are rooted in arbitrary whim.

Rather than a belief that is objective true, justified by some rigorous framework, with rationalism, truth is simply... whatever one wants it to be. To accept knowledge based on rationalism alone is to say that justification amounts to: "Because I said so."

The Solution

Ideally, knowledge comes from both. Empiricism and rationalism work together to compensate for the flaws of the other. In this debate, we ask the readers to choose which is more important on its own. Empiricism is the clear winner. The existence of an objective, physical reality allows for continual testing of beliefs. Even if we lack the capacity to think rationally about something, we can always compare our beliefs with the state of the world and discern truth from falsehood. We can form beliefs and engage in induction. We can recognize patterns and make predictions. We can construct justification based on prior observations and analysis from independent third parties.

With rationalism alone, we can do very little. We can form beliefs, yes, and all those beliefs may be "true" but only because we define them to be that way. But this truth is hollow, and devoid of import and fails to rise to the level of knowledge. Without rooting rational, logical frameworks in a physical reality separate from the mind, rationalism is little more than extensive naval gazing.

Round 3
Thanks Con for the reply.

What is Knowledge?

Con tries to make an argument for the Correspondence theory of truth and he is fortunate since I also adhere to the same theory. However, con gives a subpar argument for the theory. The main reason that the correspondence theory is correct is that a proposition is a claim about reality and so whether or not a claim is accurate is determined by whether it gives the correct assertion about the aspect of reality it attempts to describe. Moreover, words are defined by their use; and that truth is a correct correspondence to truth is just what everybody means by the word. For example, we would say that the claim "It is raining right now over the white house" would be true if it is actually and really is raining over the house. So con and I are in agreement.

Rebuttal to Con's Empirical Justification

PRO states the oft repeated criticism of empiricism that our senses are not reliable. Or, more accurately stated, they are not  infallible.

If you have been reading closely, I asserted no such thing and consequently, con is critiquing a strawman. What I said was that the fact that the senses are reliable is not something that can be established by empirical practice but is a claim that rests on philosophical foundations. So con has made a strawman out of my argument. Nowhere did I assert that the senses are not reliable. Rather, what I said was that in scenarios like some hallucination or extended dream by a Cartesian demon then our senses would be unreliable but I never said that those scenarios are actualized in reality.

Through our senses, we experience the real world and discover truths about it.

This is a loaded assumption from con. This is not where our epistemic journey ends. Under empiricism, we cannot know if the senses are reliable or if the information they are giving us reflects the external world. Some of the most brilliant skeptical philosophers like Bertrand and Descartes have taken seriously the possibility that you could be a brain in a vat being fed all of this information by a scientist or that a demon is stimulating your senses and relaying false information about the outside world or it could be that your sensory experience reflects an extended dream or a hallucination. Under these scenarios, your senses is providing you with information that does not reflect the external world at all. So con has to make some argument for the reliability of the senses. Of course, it can not be an argument that is based on sensory experience from external reality for as I have argued in my opening argument, such an argument would be circular since it presupposes the reliability of the senses in communicating the allegedly correct sensory experience that the argument is based upon. So any argument for the reliability of the senses will have to rest on non-empirical foundations in which case our knowledge that the senses are reliable comes from a method that is not sensory experience; and if con takes such a route, he would be contradicting empiricism. Since knowledge is justified true belief as con notes and since all of our justification ultimately rests on reason, then all of our knowledge ultimately derives from reason. That is the central claim of rationalism.

Rebuttal to Con’s Rational Justification

From these axioms, we can derive additional theorems. So long as the do not result in contradiction, a theorem is true. Thus a belief is true if it exists as a theorem within our logical framework

Of course as all logicians know, not all rationalists need to base their epistemological frameworks on the law of non-contradiction. Matter of fact, many systems of logic reject the law of non-contradiction such as dialetheism. Under dialetheism, a statement and its negation can both be true. So con gives an incorrect caricature of rationalism since many rationalists or philosophers who had tendencies for rationalism did not accept in the law of non-contradiction such as Graham Priest.

But where do the axioms and rules of inference come from? Easy: we made them up.

This is extremely uncharitable to rationalism. As you can see from my opening arguments, nowhere do I arbitrary make up whatever axiom I want and declare it to be true. Rather, I identified two axioms and gave rational arguments in their favour. Con should have waited to engage with the arguments given for my two axioms in his rebuttals rather than declare that I arbitrarily made them up.

Rather than a belief that is objective true, justified by some rigorous framework, with rationalism, truth is simply... whatever one wants it to be.

This claim is not even possibly true in principle because rationalism is not a theory about truth that attempts to define what truth is. We have other theories for that such as pragmatism, coherentism or correspondence theory. Rather, rationalism is a theory about how we come to discover what this objective truth is; so in a sense, rationalism presupposes what con accuses the theory of violating.

Rebuttal to Con’s Solution

This section of con’s opening arguments is a regurgitation of their earlier errors such as rationalism engaging in arbitrariness and the assumptions of empiricism. I will lend con the benefit of the doubt and avoid attacking his same points twice so I will wait to see how he responds to my rebuttals.


Rebuttal to Argument 1: "Empiricism is self-defeating."

PRO submits that the very claim of empiricism is "self-refuting." However, taken at face value, PROs complaint simply means that empiricism's claim isn't itself knowledge under the model of empiricism. Empiricists certainly believe it, and it can certainly be true, but it might lack justification and therefore not count as "knowledge."

This doesn't make the claim false and therefore does not refute or undermine Empiricism. It just means the body of empirical knowledge doesn't include the chief claim of empiricism. This is not an alien concept in logic, as all logical systems must depend on unprovable axioms. This is simply one of the unprovable axioms of empricism.

Rebuttal to Argument 2: Empiricism undermines its own evidential foundations

Similar to the above argument, PRO suggests that if the senses are not reliable then they are relaying false information. This is patently false. Unreliable simply means that we don't know whether or not the information relayed by them is false or true. If information was necessarily false, then we would be getting reliable information by simply taking the negation of whatever information was relayed to us by the senses!

Furthermore, empiricism does not require or depend upon the reliability of the senses. The claim of empiricism is that "all knowledge comes from the senses" not "everything that comes from the senses is knowledge." So long as the senses do indeed provide all knowledge, the fact that the senses also provide false information doesn't refute that. (Indeed, Gödel would explain to us that any system that is complete (derives all truths) cannot also be consistent (derives no falsehoods) If PRO wishes to levee this complete against empiricism, PRO most also explain how rationalism avoids it and claim that Gödel's theorem is false (in such a case, he has better things to be doing than debating on the internet!)

This does pose a challenge for justification, as PRO notes, but as I stated in my opening argument, empiricism deals with individual sense reliability by depending on multiple observations performed by multiple independent observers. Through this method, false beliefs are weeded out, leaving only behind knowledge.

Rebuttal to Argument 3: Rationalism as a framework

PRO again confuses unreliability for falsehoods. To say that something is unreliable is to say that we cannot know whether it is true or false. If the mind is incapable of unreliable reasoning, then the statement "the rational faculty of the mind is unreliable" would not have a known truth value. Furthermore, I will note that PRO assumes the reliability of the mind as one of the "2 axioms that undergird their epistemological foundations." PRO would seem to be in agreement with me that any logical framework depends on axioms. By their very nature, axioms cannot be proved within their own logical frameowkr (another nod to Kurt). PRO cannot simultaneously deny empiricism its axioms (such as the reality of the external world) while at the same time introducing those for rationalism.

Secondly, pro alludes to solipsism. Solipsism, as it pertains to epistemology, is that only things for which we can be absolutely certain (in a literal sense) are the only things that can be counted as knowledge. This is a very high requirement that is not universally adopted. It is certainly not a requirement stated at the onset of this debate, and it would not be reasonable to equate rationalism with mere solipsism. As such, there is no expectation for either participant to demonstrate knowledge beyond all doubt.

Lastly, PRO explains how other branches of logic can be derived from the axioms of rationalism. To this I refer to my opening argument about how such contained and insular frameworks do not count as knowledge since they are derived only by chosen axioms without any external validation. In order for something to be a true belief we must be able to distinguish it from potentially false beliefs which requires an additional criteria, an external framework. All PRO has presented are: beliefs.
Round 4
Rebuttal: Is Empiricism self-refuting?

Con decides to create a very unfortunate situation for himself here by deciding to introduce another horn to my dilemma. Now, I have argued that empiricism itself cannot be justified using empiricism and con’s response is that empiricism itself is an unprovable axiom that lacks any justification. Con here makes the key concession that there is no evidence for empiricism since it lacks any justification and thus can only be accepted through blind dogmatic faith. Con’s methodology is of course terrible, because we can declare anything we want an “unprovable axiom of our logic” be it God’s existence or even rationalism itself. If con would seriously want throw in the towel and admit that empiricism can only be accepted by blind faith since he conceded that there can be no justification for the empiricist's chief claim, then he has damaged his case by implicitly agreeing that he cannot provide any justification for empiricism.

Rebuttal: Empiricism foundations

Con here tries to shift the burden of proof he has by arguing that unreliable senses would be communicating information that we should be agnostic about rather than take to be false. The problem is that this still would not justify empiricism since we would have no way of knowing if the senses are relaying true information rather than true information, and therefore we would not know if such information is accurate. The most Con’s rebuttal proves is that we should be agnostic about the reliability of the senses rather than take them to be false. But that has been my point all along. I never said that our sensory information is unreliable, rather my point is that we have no justification to think that the senses are reliable and thus no evidence to accept such a claim unless we want to rely on blind faith. Neither could con appeal to empirical evidence to justify the senses here as I have argued above that such an approach would be fallacious.

Furthermore, empiricism does not require or depend upon the reliability of the senses. The claim of empiricism is that "all knowledge comes from the senses" not "everything that comes from the senses is knowledge." So long as the senses do indeed provide all knowledge, the fact that the senses also provide false information doesn't refute that.

Knowledge as con defined it above is justified true belief. The obvious problem is that if the senses are unreliable and deceiving us then we are not justified in using them to acquire knowledge since they are giving us false information and rather would not fit either the criterion of justified or true that is required for knowledge. As a result, the senses could not even in principle give us any knowledge and thus what follows is that “no knowledge comes or can come from the senses” which is the negation of “all knowledge comes from the senses”. Rationalism escapes this by being able to justify its own axioms as I have argued above that the denial of either axiom would be self-defeating. Con has to give us some argument for why the senses are reliable and it can not be an empirical argument because that would beg the question as I argued above.

Rebuttal: Rationalism as a framework

Con accuses me of confusing unreliability and falsehood. However, I did no such thing. My argument was for the reliability of the mind that would then entail that the mind can give us true conclusions via reason. The only real confusion lies on pro who has failed to understand what my argument was set out to prove. My argument was not set out to prove that the mind’s rational faculty always grants 100% true conclusions everytime it engages in reason. Rather, it was an argument that believing the mind to be completely unreliable would be self-defeating and false and that therefore the mind has to at least be able  to properly reason and then give us true conclusions if the reasoning is valid and the argument is sound.

A strawman for grabs

Con again accuses me of supporting solipsism but I supported no such thing. Con does not define solipsism correctly either. Solipsism is the view that your own mind is the only thing that can be proven to exist. In fact, I directly argued against such a view saying that we can be sure of other things such as the reliability of reason as well as prove the laws of logic and math using the axioms of rationalism. So I directly argued against what con accuses me of supporting and as such, his objection is a strawman fallacy. If anything, I clarified that I accept the correspondence theory of truth

Axioms and External validation

Con argues that the justification for beliefs does not lie in the claim itself but in an external reality which is precisely my view as a proponent of the correspondence theory of truth. However, I believe that reason could reveal to us some aspects of reality and knowledge that does not come from sense experience such as the laws of math and logic, the concept of “nothing”, the justification for the reliability of the senses and so on. The only real difference between rationalism and empiricism is that rationalists can justify the axioms of rationalism using argumentation while the axioms of empiricism as con concedes are unprovable and therefore lack justification and have to be accepted through blind faith.

Just a note and reminder that, as per the agreed debate structure this is my response to PRO's Round 3 argument (as well as defense and support of my own arguments).

Reliability of Senses

PRO clarifies that they aren't actually claiming that senses aren't reliable, just that the could be unreliable and that Empiricism doesn't demonstrate this. However, the senses either are reliable enough to provide knowledge or they are not. If the senses are reliable enough to provide knowledge, then PRO concedes the argument in my favor. It doesn't matter if a specific claim is not attainable by Empiricism itself (such as the claim that the senses are reliable) and is not necessary to prove the argument. The claim that all knowledge comes from Empiricism doesn't mean that all truths are justifiable as knowledge through Empiricism, just that all truths that can be justifiable as knowledge can be done so through Empiricism. There is an allowance that there are some truths that simply cannot be known.

The shared BOP also means PRO cannot simply take a neutral stance here either. They aren't just defending Rationalism, but Rationalism instead of Empiricism. To win this argument, PRO must demonstrate that the senses are necessarily reliable to a degree that no knowledge can be derived using them.

The Source of Axioms

PRO says I am being uncharitable, but does not disprove my statement. PRO says that they defended their axiom, but that does not refute my point. By definition, an axiom is "an unprovable rule or first principle accepted as true because it is self-evident or particularly useful." Thus we choose axioms because: a) they are self-evident; or b) because they are useful to achieve some specific goal. It is undeniable that the latter is a result of personal choice. I will concede that the former is not an element of choice, but self-evidence, from am epistemological standpoint, does not constitute knowledge. Furthermore, it is not necessary that a logical framework include such axioms, so there is still the element of choice that such a self-evident statement forms the axiomatic base of a given rational outlook.

Just as PRO notes that there are logical frameworks that exclude the law of non-contradiction (which many people would claim is self-evidently true), there is no reason a person can't exclude PRO's stated axioms in developing or using a different logical framework. PRO would have to demonstrate that such axioms bust necessarily be included in a given logical framework and still would have to address the fact that self-evidence isn't knowledge.

The Objectivity of Truth

PRO confirms my claim that truth requires an external basis to judge our beliefs against ("Rationalism is a theory about how we come to discover what this objective truth is"). Yet, rationalism cannot provide this. The axioms are chosen based on personal choice, as are any given rule of inference. Thus all subsequent theorems within that logical framework are a result of that choice and that choice alone. These choices strictly determine what "truths" can be derived within that framework and thus no truth can be accurately called "objective."

Without this objectivity, there is no basis against which one can judge one's beliefs to call them knowledge.

Defense and Support of Empiricism

By contrast, Empiricism, by establishing the existence of an external world through which we can attain information, Empiricism can move beyond pure introspection and judge claims against an external, objective reality that is not limited by, or subject to, our choices. The 100% reliability of senses is not required. The continued comparison of our beliefs with reality over time, and with other observers, serves to weed out potential errors. Given that 100% certain is not a universally agreed upon requirement for justification, this refinement process means that knowledge is eventually attainable.

Since knowledge can only be attained by comparison against an external, objective reality, and since Rationalism doesn't provide this while Empiricism does, only Empiricism can offer a path to knowledge.

Brain in a Vat/Hallucination Scenarios

Technically, this section only applies if PRO actually takes up the argument against the reliability of senses. The Brain in a Vat/Hallucination is a type of scenario that is oft brought up in refutation of Empiricism and similar frameworks. However, it is not given that these scenarios actually rob Empiricism of epistemological value.

Firstly: They do not eliminate the existence of an external, objective reality. The simulation or hallucination is not subject to the individual's choice or whim, so still exists as external and objective to the conscious mind.

Secondly: It does not render, strictly, false, statements made about reality itself, just our belief that the reality we are making claims about is the ultimate reality that exists, which is a separate belief. For example, if you project the holographic image of an apple on a table and I say, "there is an apple on the table," yes that statement is technically false, as the apple is fake, but bound within that simple statement are a number of implicit facts:

1. There is something there on the table.
2. It has the size, shape, and color of an apple.

So even if the statement itself, taken at face value, isn't itself knowledge, knowledge is still attained in some form.
Round 5
The Reliability of the Senses

Con here thinks that I am saying that the senses are reliable and he would be correct but the implications of my claim
not concede anything to his position but rather directly undermines his position. My position on the reliability of the senses is that they are reliable but that this knowledge comes true on the basis of rational not empirical arguments. So my position that this knowledge comes to us via reason not the senses is in direct contradiction to empiricism and most certainly does not concede anything to empiricism. My problem was that empiricism itself cannot justify this claim which is crucial to its foundations. Con also tries to redefine empiricism by saying that "all truth that can be known as knowledge can be done so through empiricism". That is not the definition provided that empiricism just is the claim that all knowledge does come from the senses. What can happen and what does happen are not the same and so Con is attempting to redefine the words laid out.

Sources of Axioms

Con creates a false dichotomy that axioms can be inferred on the basis of self-evidence or being useful. Of course, that is not how I defend the axioms of rationalism. I defend them on the basis that denying them would be completely self-defeating and so such a position would be untenable.

PRO would have to demonstrate that such axioms bust [sic] necessarily be included in a given logical framework

What Con brings up here is actually a key component of rationalist worldviews to choose the right system of logic. However, whether or not I personally choose the right logic system is irrelevant to whether rationalism is true. Rationalism could be true even if I believe the wrong system of logic.

Now a problem for Con is that while I can justify the two axioms that undergird rationalism, Con has repeatedly struggled to justify any of the two axioms of empiricism and has provided no evidence to suppose that the axioms of empiricism are true. That's the main difference between rationalism and empiricism. The former can justify its own assumptions and axioms; the latter has to accept them on the basis of blind faith.

The Objectivity of Truth

Con keeps regurgitating the same point that rationalism rests on axioms that are determined by personal choice. However, if you have read my opening arguments, I do give a thorough argument for the existence of the mind and the reliability of its rational faculty. Con has not only failed to address this argument but almost seems unaware of their existence which would explain why he keeps repeating that the axioms of rationalism are held on the basis of personal choice. The justification for each claim, under rationalism, would be the rational argumentation given for the claim, which would eventually trace down to more fundamental axioms.

Defense of Empiricism

Con here tries to give some sort for Empiricism. The argument fails on multiple fronts. First of all, the only way to attain truth under empiricism is sense experience. Since con conceded above that empiricism cannot be established through sense experience, then empiricism lacks justification and is devoid of evidence putting it in the category of blind faith. A claim that rests on blind faith sans justification is not a rational one to adopt.

Secondly, we have no way of knowing whether con's claim that sense experience allows us to test a claim against reality, under empiricism. Con up until now has failed to give any argument whatsoever to justify the reliability of the senses. If assuming the reliability of the senses is unjustified due to lacking evidence, then we are deriving our knowledge from an unreliable unjustified source. The problem for
is that no empirical argument can be given for that claim and it can only be proven philosophically. So con's claim that empirical evidence or sensory experience allows us to fact-check our claims against reality has enjoyed no justification from con's side since he could not provide any evidence that empirical evidence or sensory experience is reliable.

It is not clear that Rationalism provides us with no way to check if our claim is reliable and reflects reality. All the rationalist has to do is provide a sound rational argument for the claim and he has done his job.

Brain in a vat / Hallucination

Traditionally, the rationalists have used the brain in a vat argument to show that rationalism can address skepticism while empiricism crumbles under skepticism. If the external world that the mind is picturing is illusory and the external world is completely different; due to being fed illusory information by say, a mad scientist, then our senses give us no trustworthy knowledge. Rationalism can address this by pointing out that sensory experience was not needed to know anything to begin with; since we can get by on the rational faculty of that mind. So while I do not endorse the brain in a vat scenario, I think it offers a good piece of evidence to
rationalism over empiricism.

The second point that Con makes conflates appearance and reality. Hypothetically, you could be driving on a hot day and hallucinate a mirage on the road. Not even the rationalist doubts that it appears like there is a real mirage but your perception here is mistaken because there is absolutely no water whatsoever on the road despite what your senses are telling you. So in this case, the senses are supplying you with information such as the mirage on the road but the reality of the matter is that the appearances are contradicting reality and so are not true and can not be called knowledge in any meaningful sense.

Closing Remarks

Aristotle in the opening of his Metaphysics says that all men by nature desire to know. That's the biggest reason why we should oppose empiricism. Under Empiricism, knowledge becomes impossible since it all rests on unjustifiable axioms that we have no way to verify through empiricism, such as the reliability of the senses, the reality of the external world, the correlation between mind and reality and the existence of the mind. All knowledge becomes the projection of blind faith which lacks any justification and as con himself has told us one of the criteria for knowledge has to be justification. Not only does the claim "all knowledge comes from the senses" contradict our knowledge of mathematics, logic and other a priori fields but empiricism itself is not a claim that comes from the senses making it self-defeating. 

Vote Pro.
Note: This is a Response to PRO's Round 4 Argument.

Defense: Is Empiricism self-refuting?

PRO latches on to my claim that all logical systems (including Empiricism) must include unprovable axioms. PRO agrees with this implicitly. The definition of axiom is widely known and, within the context of this debate, uncontested. PRO admits that even Rationalism is based upon axioms. I do not concede that the existence of axioms as a foundation for a system of logic means that said logic "lacks any justification" or requires "blind dogmatic faith." None of the arguments PRO presents here would be unique to Empiricism, as PRO notes ("we can declare anything we want an 'unprovable axiom of our logic' ... even rationalism itself.")

Defense: Empirical Foundations

PRO continues to assert that the senses must necessarily be reliable in order to derive justification for knowledge from them. This is patently false. Consider, first, what reliability means. Reliability requires consistency. Even if our senses provided false information, if they provided false information consistently, we could account for that. For example, if every third observation was false, then we could discover that and dismiss every third observation. Since falsehood is the negation of truth, consistently providing false information is just as good as consistently providing true information, and the senses would become reliable.

What does that mean for unreliability? It means that the accuracy of observations, and their truth and falsehood would have to be inconsistent. Most importantly: if the senses provide incorrect information, then they must do so in an inconsistent and random manner. This is key. It means we are permitted methods of weeding out bad data.

Firstly, whenever the senses are true, they will necessarily be consistent because the truth does not change. Whenever the senses are false, they will be inconsistent as per the argument above. Thus, with repeated observations over time and across many different observers, the static nature of the truth will be noticeable about the random white noise of falsehood.

Second, by temporarily assuming the truth of our observations we can made predictions. If those predictions turn out to be true, that supports the the original observation. The more predictions that are made that come out to be true, the more reliable those observations become. The likelihood that an observation and large number of predictions would be incorrect in the exact manner necessary to give the illusion of truth is small enough to be not worth consideration.

Rebuttal: Rationalism as a Framework

PRO presents the argument that while the unreliability of the senses somehow defeats Empiricism, PRO sees no problem accepting the unreliability of the mind with respect to Rationalism. This position is incongruous. The senses and the mind serve exactly the same purpose within their respective frameworks. PRO cannot lobby one argument against one without it also applying to the other. Unless PRO is willing to argue the unreliability of the senses (they aren't) along with the reliability of the mind (they aren't) then that is a necessary concession that Rationalism fails where Empiricism succeeds.

An aside: I did not say PRO "supports" Solipsism. I said that PRO "alluded" to it.

More importantly, PRO agrees that justification requires an external reality against which to measure the truths produced by a logical framework. Rationalism provides no such framework! The truths of rationalism are based only upon logical inferences derived from chosen axioms! PRO suggests that the axioms are rationalism are derived from argumentation, but this contradicts what an axiom is: an unproven statement taken to be true!