A review of the SEP article of epistemology indicates that there are 5 sources of knowledge: perception, memory, introspection, reason, and testimony. Robert Audi in his Epistemology: A Contemporary Introduction to the Theory of Knowledge cites an almost identical list substituting 'consciousness' for 'introspection'. (NB: the article cites Audi as a source.)

Is this ontology of five kinds of sources of knowledge universal, or is it just one perspective perhaps unique to a subset of thinkers in the analytical tradition?

  • 3
    Natural kinds are controversial to begin with, one has to subscribe to Kripke-Putnam's essentialism, or something like it. Phenomenologists reject the identification of consciousness with introspection, as well as the idea that a meta-study, like epistemology, can be subordinated to the results of positive science. Quine himself had to address concerns about circularity. According to them, his addressing fails. See a phenomenological critique of naturalized epistemology by Rinofner-Kreidl in the Feist volume.
    – Conifold
    Oct 9, 2019 at 17:56
  • Thanks. Already ordered it. (For others, the essentialism is mentioned in plato.stanford.edu/entries/essential-accidental)
    – J D
    Oct 9, 2019 at 22:35
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    The Indian school of logicians, the Nyaya school, have a slightly different approach. Chapter 12 here - archive.org/details/IndianPhilosophyACriticalSurvey Oct 10, 2019 at 10:46
  • "For instance, is the philosophy of language really distinct from the philosophy of psychology"; well, depends on what you take for philosophy of psychology. Often it is common to subscribe most of the sciences to neuroscience and psychology, but that is quite controversial. Oct 13, 2019 at 10:37
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    It would help if you focused on a single question - your three questions cover too much ground for a manageable answer, in my view.
    – Geoffrey Thomas
    Nov 16, 2019 at 13:28

5 Answers 5


The SEP article is based on the assumptions of analytic philosophy, that empiricism and reasoning are the valid methods of acquiring knowledge. Its 5 categories are not a narrow approach to analytic thinking, but instead reflect what appears to be an effort to include multiple schools of analytic thought. However, there are several major categories of analytic philosophical thought that still are not included in these five categories.

The most noteworthy is direct apprehension. IE -- that humans have direct intuitive access to reality, and can know it without reason nor inference -- DIRECT realism. Many non-analytic philosophers hold by intuitive knowledge. And while analytic philosophers often disparage intuitionalism -- a major subset of them are direct realists, who are asserting intuitionalism explicitly. And in addition to the direct realists, pretty much all analytic philosophers hold faith in reasoning, and in materialism, despite not being able to justify either (in particular, the justification for reasoning cannot pass Munchausen's Trilemma) -- IE these are intuited assumptions, and therefore fall outside the suite of 5 sources of knowledge listed.

A further issue within the article is that it assumes that JTB is a valid condition for it -- despite NOTHING being able to satisfy JTB when one applies Munchausen's Trilemma to the justification.

An analytic philosopher who accepts that JTB is invalid, and worked to build an approach to knowledge that lives with the Trilemma is Karl Popper. Conjectures and Refutations is a good representative collection of his essays that could give you some additional insight into questions of epistemology.

  • Thanks. I think this addresses the nature of the question very well in regards to what conceptions are built automatically into the SEP article, and perhaps what are some lines of attack that can be considered on those presumptions.
    – J D
    Nov 4, 2020 at 15:12

Readings in Formal Epistemology, a source book, ed. Arló-Costa H. et. al, Springer 2016 - this seems to match your introductory stipulation(s).

Also, browsing through it, there is a good chance to conclude that what we can read in the otherwise respectable SEP is of little worth. Calling these 5 kind of sources an "ontology" seems a misunderstanding as they are just numbered items from a vaguely persuasive narrative that might get bogged down in complications. The approach is seen to derive mostly from the failure of JTB which some time ago enjoyed popularity. (Belief and knowledge are substantially different in many languages)

As an alternative you could look at the topic through the concept of information which is really fashionable just now. There has been indeed a proposal to eliminate (or reduce) knowledge to information.

Jaakko Hintikka is a thinker not exactly in the analytical tradition but rather tangential to it, and he has been something of pioneer, so I would recommend to look at his work e.g. Knowledge and Its Objects in Plato, the opening chapter of Knowledge and the Known (Springer 1991). In the source book you could read his Epistemology Without Knowledge and Without Belief at least to get some feeling about the plurality of perspectives.

  • Much obliged. Thank you for a stepping stone.
    – J D
    Oct 30, 2020 at 16:51
  • I awarded the bonus based on that the text you offered seems to offer the widest variety of sophisticated forays into the nature of the question on where epistemologists stand in general. Thanks again!
    – J D
    Nov 4, 2020 at 15:13

Knowledge is necessarily more fundamental than whatever we call perception, memory, introspection, reason, and testimony. Thus, these five items should indeed be regarded at best as sources of knowledge, and then only potential sources of knowledge.

And then of course there is a snag. Suppose you want to say that perception is a source of knowledge, then of course the question comes: How do you know that?

This suggests that these five sources are not sources of knowledge but sources of belief. I may be able to consult my memory of yesterday, but this does not imply that I will thereby know what happened yesterday, not even to myself. All I will get is the belief of what happened yesterday.

There is just one form of knowledge which we cannot deny and this is the knowledge of whatever subjective impression we have: impression that the sun is shining? Maybe the sun is not in fact shining but I sure have the impression that it is. Impression that I am in pain? I may be wrong to infer that maybe I cut my finger or something, but I cannot deny that I have the impression of it.

So this means the only source of knowledge is subjective experience. Our subjective experience gives us knowledge of our memories, perceptions, reasons etc. And then we usually proceed by believing that these sources of belief truthfully represent something real, as it is, so to speak.

There are all sorts of views on the sources of knowledge, including divine revelation and what not. Your list of five is missing intuition for example, even though it is one of our major source of belief, one we use even more heavily than memory or reason. Maybe you could put down intuition as a species of introspection but no, this is not the same thing at all.

Perception, does it include "feelings" and "sensations", both providing us with beliefs about our own body?

Does "reason" include "logic"? Presumably, somehow, yes, but logic, nonetheless, is distinct from reason.

These different sources of belief are essentially contingent to us being natural cognitive systems. This list of five sources sounds like the list of the four fondamental elements, air, water, earth and fire. Not exactly entirely false, but somewhat naïve. A first approximation. Knowledge is more fundamental.

In fact, why would we even need to define knowledge to begin with? No definition will ever detract or add anything to our knowledge of something whenever we know something. The effort of analytical philosophers to define knowledge in terms of belief, truth and justification thus appear to be futile efforts to turn belief into knowledge, somewhat like the alchemists once upon a time pretended to turn lead into gold.


1.Is this argument misconceived or is this inference correct, or are there other contributing lines of inquiry to the ontological foundations of epistemology? For instance, is the philosophy of language really distinct from the philosophy of psychology to an extent that it should be on a list?

If ontology means the existence rather than the knowing it's a presupposition. The presupposition is the distinction between knowledge or representation on the one side, and being that is known. Where does the presupposition happen? In an academic circumstance the blind bigotry of a reception out of one's training determining the whole output is in play and a factor not to be underrated in its sheer power.

Psychology means literally the reasoned discussion about the soul. When it becomes experimental psychology it is simply the study of one experimental object that is no different from others in its status as experimental object.

Language can be studied as a matter of signs referring to beings. Thus under a presupposition of knowledge and things. In the German tradition, however, it is not studied in this manner since Husserl's concept of intentionality sets this presupposition aside.

2.Do those who argue against Quine's naturalized epistemology or moderate positions thereof reject that the philosophy of psychology and the science proper are an ontological basis, and if so, who and by what lines of attack?

If one treats logic as ontologically real, one can set everything else aside as mere subjective or psychological error. Thus, the claim that "not being is" has no ontological status, I look and see that something is positively not there, the not being is a positive fact, something is missing, but are the mere product of psychological appearances is only psychologically valid. Nothing is nothing for logical proof. The faith in the ontological reality of logic prevents the need to go to Phenomenology. Ultimately it is unsatisfactory and ever serious student of philosophy arrives at this view, as did Russell, because of the problem of primary intuition which happens prior to any logical neatness, but some still hold "logic" is more promising than abandoning the possibility of "knowledge" (which is no longer knowledge once it is accepted that logic is not a being, but a figure of subjective creation) of a repetitional kind for the dark path of phenomenology.

3.Do phenomenologists have a different approach to establishing the ontological foundations of knowledge given they do not subscribe to the importance of physicalism, and hence the brain, which is taken in the analytical tradition as that upon which the mind supervenes?

Phenomenology is based on radical disregard of a claim to a specific ontological priority. Say of the subject matter of physics. This is possible because of the denial of a project of possible representational knowledge. The knowledge would only consist in direct observation of the transformation of the phenomena. Phenomenology is the result of the Cartesian ultimate doubt without the project of building up from the doubt to a science. One starts with and stays with the doubt. Questions about the brain can still be asked, but judgment about any privileged foundation of phenomena are set aside.


'I am curious about lines of thinking which look at epistemology through ontological lenses specifically.'

Proposition 5 from Spinoza's "Ethics" Part 2, (below) needs a bit of transliterating, but does predate by over 300 years your assumption that your 'list' includes every ponderable concerning the origin and nature of epistemology in ontology. Spinoza's use of the word 'god' is confusing but it would not be incorrect to describe god as, 'the first metaphysical principle and self-caused origin of the entirety of everything possible'. Sounds like an artificial catch-all phrase but it is not. The capacity to know, to think and to self-reflect mark humans as distinct from anything else in nature. Spinoza recognized that in his capability to reflect on the origin of human thinking he was experiencing not some random happenstance, illusion, dream or phantasm, but was participating in a function of 'universal intelligibility'. No matter how I might express this idea, only you can examine for yourself his philosophy and decide if indeed he is correct. Best of luck.

Prop. V. "The actual being of ideas owns God as its cause, only in so far as he is considered as a thinking thing, not in so far as he is unfolded in any other attribute ; that is, the ideas both of the attributes of God and of particular things do not own as their efficient cause their objects (ideata) or the things perceived, but God himself in so far as he is a thinking thing. Proof.—This proposition is evident from Prop. iii. of this Part. We there drew the conclusion, that God can form the idea of his essence, and of all things which follow necessarily therefrom, solely because he is a thinking thing, and not because he is the object of his own idea. Wherefore the actual being of ideas owns for cause God, in so far as he is a thinking thing. It may be differently proved as follows : the actual being of ideas is (obviously) a mode of thought, that is (Part i., Prop. xxv., Coroll.) a mode which expresses in a certain manner the nature of God, in so far as he is a thinking thing, and therefore (Part i., Prop. x.) involves the conception of no other attribute of God, and consequently (by Part i., Ax. iv.) is not the effect of any attribute save thought. Therefore the actual being of ideas owns God as its cause, in so far as he is considered as a thinking thing, &c. Q.E.D."

All the Best, Charles M Saunders

  • I don't do theism, but I wanted to demonstrate no hard feelings. My beef is with your characterization of science, not you.
    – J D
    Dec 16, 2019 at 1:15
  • @JD- Same here. Spinoza did not 'do' theism either. He was first and foremost a scientist. He manufactured what in his day were the finest lenses for microscopes in Europe. Christiaan Huygens, (Father of Mathematical Physics) and Spinoza collaborated on Optical theory and lens design. Leibniz traveled to Netherlands and sought out Spinoza. Spinoza was a friend and communicant with Henry Oldenburg, the first Secretary of the Royal Society and he exchanged a number of letters with Robert Boyle Father of Modern Chemistry. A book on his use of Geometry; Spinoza's Geometry of Power, V Viljanen. CMS
    – user37981
    Dec 16, 2019 at 17:15
  • Anyone who does God or gods is a theist: "These are the fundamental concepts with which Spinoza sets forth a vision of Being, illuminated by his awareness of God. They may seem strange at first sight. To the question "What is?" he replies: "Substance, its attributes, and modes". — Karl Jaspers[89]
    – J D
    Dec 16, 2019 at 21:27
  • His "science" is 400 years old, so historically noteworthy, but at a best a contribution to contemporary philosophy. It was certainly typical of the leading men of science 400 years ago to harbor belief in an impersonal God. Less prevalent today. pewforum.org/2009/11/05/scientists-and-belief
    – J D
    Dec 16, 2019 at 21:47

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