In popular discourse, knowledge implies certainty. In most cases, when a person speaks of “knowing” or “having knowledge” of something, that person is asserting that he or she has true beliefs regarding that thing. While there are exceptions, and some individuals treat, say, the reasonable probability that something is true as constituting knowledge, for the most part when people assert that they “know” a statement is true, they mean they are certain of that statement’s truth.

However, full certainty never exists in practice, even regarding the truth or untruth of analytical propositions, that is, proposition the meaning of which can be found solely by reference to the terms of the proposition in question. Regarding synthetic propositions, or propositions which depend for their meaning on some interaction or relationship with the world of experience, there is greater uncertainty still.

For these reasons, I prefer not to speak of knowledge but of apparently justified belief.  This term, while wordier than the term “knowledge,” clarifies that no beliefs, no matter how robust and verifiable they seem, and no matter how certain those who believe them claim to be, are ever held with certainty.

I say all beliefs that seem justified are only apparently so because it is always possible to doubt any belief one holds—in other words, no belief is held with certainty. Even the belief that “I exist,” famously held out by Rene Descartes as the one undoubtable belief, can be doubted for the simple reason that the “I,” that is, the sense of distinct individual identity that every person has, is arguably merely another object arising within a pure consciousness devoid of any sense of individuality or unique identity. On the other hand, while the experience of pure consciousness, in which neither any object nor any sense of distinct individual identity arises, cannot be doubted (in fact, no experience devoid of propositional content can be doubted), as with any experience, any interpretation of the significance of such an experience can be doubted.

Based on my experiences and my studies, I have found there to be approximately eleven sources of apparently justified belief. Some of these source-categories may be collapsible into others. These source-categories should be treated as general guidelines rather than rigid distinctions, although I believe that the distinctions drawn here are useful in clarifying the fundamental issues of epistemology.

The First Source of Apparently Justified Belief: Simple Identity

As discussed in my post “The Laws of Thought,” the Law of Identity is one of the three classical laws of thought formulated by Aristotle. In simple form, the Law of Identity means that a “thing is itself,” which can otherwise be expressed as “A is A.” On the surface, this seems to be the most straightforward analytical proposition imaginable. It seems quite reasonable to assert that one “knows” that “A is A” rather than merely that one is “apparently justified” in believing it.

However, terms change meaning across time. What is defined as “A” one day could end up meaning “B” the next. More realistically, what is defined as “A” in one era can slowly come to mean “B” several centuries later. Because of the shifting meaning of referents like “A” and “B,” it is not possible to say that one knows that “A” is “A.” “A” might in fact be “B.” However, we appear to be justified in believing that “A” is “A,” but not because coherent discourse is impossible without this belief (the fact that coherent discourse is impossible without this belief does not mean that this belief is true; coherent discourse may, in fact, be impossible, though I am mindful of the fact that this would mean the words I am using here are not coherent and that I am foolish for writing them).

We appear to be justified in holding this belief because in our experience, what we call a “chair” has certain features which we can identify when we encounter an object we understand to be a “chair,” features which automatically signal to our brains that we are in the presence of a chair, such as a seat and a structure of some sort which grounds that seat on the floor or soil.

The Second Source of Apparently Justified Belief: Tautology

A tautology is a statement that is true by definition, that is, by the very meaning of its terms, though the relationship between the terms of a tautology is not one of simple identity. An example of a tautology is the statement “all bachelors are unmarried.” Of course, a “bachelor” is by definition a person who is unmarried. However, our understanding of the terms “married/unmarried” and “bachelor” depends on our interactions with the world, as marriage is a social institution that cannot be understood apart from the social practices that define it, while bachelorhood only exists in relation to the social practices that define marriage. All tautologies similarly depend on our interactions with the world.

In terms of attempting to establish a basis of justified belief, tautologies have the same problem as statements of identity: terms change meaning across time. We appear to be justified in holding the belief that all bachelors are unmarried based on our current definitions of these terms, and we can even claim to know this is true at present, based on these current definitions. However, the fact that it could be possible to know that this statement is untrue in the future (if the definitions of these terms change) arguably calls into question whether it is justifiable to call our present state of awareness one of knowledge. For if a state of “knowledge” can turn to a state of “not-knowledge” over time, it calls into question whether it is coherent to speak of the state in question as one of knowledge in the first place.

The Third Source of Apparently Justified Belief: Deduction

Deduced propositions are on a sort of middle ground between analytic and synthetic. To be valid, deduced propositions must first conform to the axioms of some prior system of logic or even semi-logic. However, if they have content that can only be confirmed or disconfirmed by experiences of the world outside that system of logic or semi-logic, these propositions must also agree with the data of the external world.

The axioms of no system of logic that purports to accurately describe the external world of experience can be proven to actually describe the external world of experience from within that system, but only by reference to experiences of the external world. Put a different way, a deduced proposition within a system of logic or semi-logic that purports to have content that can be confirmed by experience, while it can possibly be proven true within that system of logic or semi-logic, cannot possibly be proven true of the external world without an actual experience of the external world that confirms its truth.

Take the syllogism “All men are mortal. Socrates is a man. Therefore, Socrates is mortal.” It is not possible to understand what a man is, what it is to be mortal, or what or who Socrates is without interacting with the world of experience. To be a man is to be a member of the species homo sapiens sapiens (while there is even some room for argument about this statement, it is conventionally true), to be considered to have passed into manhood by the conventions of one’s society, and to either identify with the male gender or have male anatomy (depending on the context), all of which can only be understood by reference to actual experiences of actual men. To be mortal is to die. Mortality, like manhood, is only understood by reference to actual experiences of death, of organisms dying. The historical person represented by the word Socrates can only be understood by reference to either historical texts or orally transmitted stories about that person. So, the syllogism above and the deduction that flows from it depend completely on interactions with the world of experience.

Because it is always possible that one is mistaken about the content and/or significance of one’s experiences, the validity of all experiences can be doubted. For this reason, the truth of every deduced proposition that ostensibly has experiential content can be doubted as to its experiential validity, even if it is valid in a strictly analytical sense. Deduced propositions lacking in experiential content (if they exist) are basically just tautologies. As tautologies have already been examined, I will not rehash my discussion of them here.

The Fourth Source of Apparently Justified Belief: Sensory Perception

The fourth source of AJB is sensory perception. As it sounds, sensory perception refers to the processing of sensations or sensory inputs by the brain. First comes the sensation, whether with the eye, ear, skin, or any other organ of sensation. Then comes an electrical signal from that organ to the central nervous system, which processes the signal and interprets it as an experience of a particular sensation or combination of sensations. No sensory experience occurs in a vacuum. Most sensory experiences both depend on and reinforce one’s prior interpretations of the world, while new sensory experiences modify one’s previous interpretations. Sensory experiences are never purely empirical, in other words. They always involve a priori interpretive mechanisms, which appear to be innate in the human mind.

Beliefs are formulated on the basis of sensory perception either as a direct result of such experiences, or as a result of inferences drawn from such experiences. An example of a belief formulated as a direct result of an experience of sensory perception is the belief that fire is hot to the touch. Another example is the belief that roses have a pleasant smell, though this belief is a matter of opinion and cannot possibly be established as universally valid, even though most people would undoubtedly agree with it. On the other hand, the former belief seems hardly open for dispute. Nonetheless, as extremely unlikely as it is, it is not possible to completely rule out the possibility that our skin deceives us and fire is not in fact hot to the touch. It is also not possible to completely rule out the possibility that the sensation that we call “hot” has the same general feeling as what others sense as “cold,” and that these designations are thus subjective and not universally valid. These possibilities sound ridiculous, and probably are, but it is not possible to rule them out altogether. For this reason, I assert that the belief that fire is hot to the touch, while it is in accordance with everyone’s or almost everyone’s experience, is only apparently justified.

We draw inferences from our sensory perceptions on an almost daily basis. For instance, we infer that the sun will rise on future mornings because we have seen it rise every morning in the past (assuming we live south of the Arctic or north of the Antarctic Circle). While the belief that the sun will rise on future mornings is very likely true, it cannot be known to be true with certainty. We are again only apparently justified in believing that it will. Shifting gears slightly, it is worth noting that most of science consists of drawing inferences based on sensory perceptions, whether those perceptions are mediated by machines and measurement devices or not. Science can proceed by either deduction, induction, or a complex combination of the two.

The Fifth Source of Apparently Justified Belief: Extrasensory Perception

The fifth source of AJB is extrasensory perception. This source is often treated as illegitimate because of the extreme difficulty of confirming even a single claim of extrasensory perceptive experience. However, just because the validity of such experiences is difficult to confirm does not mean that those who believe they have had them are not justified in believing that they experienced something which cannot be explained by reference to known natural properties or the perceptions of the physical senses.

It is certainly prudent to consider the possibility that one has made a mistake when one has an experience that seems to include or consist wholly of some manner of extrasensory perception, and to not rule out the possibility that one is mistaken unless and until one has overwhelming evidence in the likelihood that one is not. But if one has an experience that can only be effectively explained in terms of extrasensory perception, or even if this is the best of several competing explanations for an experience, then one is apparently justified in forming beliefs in the existence of whatever extrasensory phenomena one seems to have experienced.

Before moving on, I would like to point out that it is not “skepticism” to doubt the validity of extrasensory perception as a means of acquiring beliefs about the world or to trust sensory perception as a means for acquiring beliefs about the world. Skepticism in the true sense of the word means an attitude of doubt towards all beliefs, including all of one’s own provisional beliefs and stances. In other words, it is not a synonym for naturalism, scientism, or empiricism.

The Sixth Source of Apparently Justified Belief: Induction

Induction means reasoning from a particular experience or observation, or a particular set of experiences or observations, to a general principle. It is one of the main ways scientific explanations are arrived at. When used as part of the scientific method, induction consists of postulating general laws, theories, and principles on the basis of data and/or observations gathered over time. In daily life, induction refers to arriving at general explanations on the basis of one’s particular experiences.

Many thinkers have recognized that induction is problematic for a variety of reasons. David Hume famously recognized its limitations. The best way to illustrate it is the “white swan” problem. If one does not live in Australia or has never been to Australia, then it is very likely that all of the swans one has seen are white. A person who has only ever seen white swans may conclude on that basis that all swans are white. Even if that person has seen 10,000 or 100,000 white swans and has never seen a single black swan, this does not prove that all swans are in fact white. It may lead to that inference, though of course the inference in this case is fallacious, as there are black swans. (And yes, as usual, no matter how remote the possibility, it is nonetheless possible that all humans who have seen what they take to be black swans or even white swans are mistaken, either through deception of their visual faculties or by some other means, and that all swans are yellow and purple.)

The problem of induction applies to all particular experiences in the same way. There is never any way to know with certainty that the general principles one formulates based on a plethora of consistent particular experiences accurately reflect the way things are.

The Seventh Source of Apparently Justified Belief: Inference

Inference is a means of approximating an as-yet unexperienced state of affairs by comparison with an already experienced state of affairs.

For example, where one sees smoke in a forested area but does not at the same time see fire, it is still possible to infer that there is a fire. This inference is based on previous experiences (whether one’s own or those of another whom one trusts), where smoke and fire have been observed together, and specifically experiences where a forest fire has been observed to cause smoke. In many cases, this inference is also based on the (incorrect) belief that smoke only ever occurs when there is a fire to cause it, which arises as a result of never having experienced smoke without fire (or never having paid attention when one had the opportunity to observe smoke without fire). Inference thus depends on previously established apparently justified beliefs, here the beliefs that fire causes smoke and that smoke in a forested area indicates that there is a fire in the forest.

Inference is also possible with extrasensory perceptions, assuming they are in fact extrasensory perceptions and not the result of imagination. But because shared experiences of these apparent perceptions are so rare, it is difficult to argue that inferences based thereon are reliable in providing information about the external/mutually experienceable world. Even if these apparent perceptions do not provide reliable information about the external/mutually experienceable world, they can at least provide reliable information about the workings of a person’s imagination.

The Eighth Source of Apparently Justified Belief: Analogy

Analogy is a means of explaining the attributes or nature of one thing by comparison to another thing.

In most cases, beliefs are not formed based on analogies. Instead, analogies are typically used to illustrate or explain previously developed beliefs or previously considered ideas through a comparison that renders those beliefs or ideas less abstract and more tangible to the person trying to explain them and/or the person to whom they are being explained. Thus, many analogies attempt to explain a relatively complex or abstract idea by comparison to a seemingly simpler idea, though it is of course possible to draw analogies between something relatively simple and something more complicated, as well as between equally complex ideas.

However, because beliefs can be formed on the basis of analogies, analogy is a potential source of apparently justified belief. For example, theologian William Paley’s analogy between the idea of an intelligent designer/creator of the universe and a watchmaker as a basis for believing in the actual existence of an intelligent designer/creator is one of the most famous in the history of philosophy. While it is debatable whether anybody has ever come to belief in a designer/creator of the universe as a direct result of considering this analogy, it is at least theoretically possible to do so. Thus, I will use it to illustrate analogy as a source of apparently justified belief.

Paley’s argument from design is that just as a watch’s complexity necessarily means that an intelligent being made or designed the watch, so the complexity of a feature or the totality of the physical universe necessarily means that an intelligent designer designed or created that feature or even the totality of the physical universe. I hold the belief in the possibility that the universe was created or designed by an intelligent being to be apparently justified, for while there is no empirical evidence for or against the existence of an intelligent designer or creator either way, as the theologian Paul Tillich put it, there is “something rather than nothing.” It is possible that the watchmaker analogy could also lead to this apparently justified belief, but on the grounds that the universe might be analogous to a watch in the manner described by Paley and his followers rather than on the grounds that there is something rather than nothing.

(As an aside, to avoid confusion about my theological position I will clarify here that belief in the possible existence of an intelligent designer or creator, and even belief in the actual existence of an intelligent designer or creator by itself would not warrant belief in even the most basic teachings or underlying premises of any religious or philosophical tradition that I am aware of, as every major theistic religion and theistic philosophical tradition that I am aware of teaches not only that there is a creator, but contains a wide range of other beliefs, premises, and practices that the tradition in question holds people must embrace for their lives, minds, bodies, and societies to know and reflect the truth.)

The Ninth Source of Apparently Justified Belief: Introspection

Introspection is the examination of the contents of one’s own conscious experiences using the “mind’s eye,” i.e. the faculty of experience that looks “within” at the “internal” world of one’s own consciousness rather than “without” at the seemingly “external” world of physical objects and fellow conscious subjects. (While the belief that there is a real world full of real objects and fellow conscious subjects that can be known to truly exist by any unbiased experiencing subject who comes along is a fallacious belief known as naïve realism, in practice almost people are naïve realists, at least some of the time.)

Based on introspection, one can learn how one responds to stimuli, such as sensory perceptions and thoughts. Thus, for example, if thinking about a certain subject causes one to feel anger, one is then apparently justified in believing that thinking about that subject causes feelings of anger to arise. However, beyond such straightforward examples, the reliability of introspection in forming apparently justified beliefs, particularly about mental processes of which one is normally not consciously aware, becomes questionable.

It might be possible to examine the contents of one’s consciousness at far deeper levels than one’s responses to stimuli, but it is difficult to determine how accurate “examinations” of this sort are, as there is no neutral standard against which to check them. It is difficult to even say for sure that there are “deeper” levels of consciousness. While the belief that some mental processes are unconscious is apparently justified based on the best available evidence, this does not mean that those unconscious processes are “deeper,” in either the sense of more fundamental or more important, than what one experiences in one’s ordinary waking state.

It is also not clear to what extent introspection is overlain with presumptions that prevent one from examining the contents of one’s consciousness in an unbiased way, though my educated guess is that this happens frequently, possibly even every time anybody practices introspection. At the same time, it is possible that introspection can be unbiased, in which case it could in theory make one aware of all of one’s presumptions and biases.

Still, it is difficult to define the scope of what beliefs are and are not apparently justified on the basis of introspection, or to determine how biased or unbiased a person’s introspection is in the first place. Introspection is thus deeply problematic. Its validity is almost impossible to establish because it cannot be checked against others’ experiences of the same thing, as introspection can only ever, as far as I know, examine the mind of the person engaging in it.

The Tenth Source of Apparently Justified Belief: Direct Experience

 As I use the term, direct experience refers to experience as a particular mode or state of consciousness or existence rather than experience of an apparent object of consciousness.

Beliefs based on direct experience are beliefs about the very nature of consciousness as a present lived reality, not beliefs about consciousness in the abstract. These are beliefs in the very nature of subjectivity, as well as in aspects of consciousness that feature neither the sense of subjectivity nor the sense of objectivity.

Beliefs are formed on the basis of one person’s direct experiences only as a direct result of that person’s experiences themselves, not as a result of inferences drawn therefrom. While direct experiences must still be interpreted for beliefs to be formed on their basis, all that we are apparently justified in believing based on direct experiences comes only from within these experiences themselves. Anything beyond that is pure speculation and is thus not apparently justified.

An example of an apparently justified belief formed based on direct experience is the belief that the deepest or truest level of the self is a state of consciousness in which neither any sense of separate selfhood nor any object of consciousness arises.

Another example of an apparently justified belief formed based on direct experience is the belief that present consciousness is the consciousness of a distinct and separate personality, that is, a distinct and separate conscious subject. The view that there are other conscious subjects is based on inference, not on direct experience, as other seemingly conscious subjects are experienced as objects in each particular stream of awareness.

Direct experience is problematic for the same reason as introspection. It is difficult or even impossible to check one’s own experiences as a mode or state of consciousness against others’ direct experiences as the same mode or state of consciousness. Even if all people can in principle have such experiences, there is no way to confirm that one person’s direct experience is the same as another’s, even if the language used to describe them is similar or identical.

Based on similarity of language, it can perhaps be inferred that one direct experience is like another, but without experiential evidence of some kind for this inference, one is not apparently justified in forming beliefs on its basis of this inference, as such beliefs are the result of pure speculation.

The Eleventh Source of Apparently Justified Belief: Imagination

The imagination is the faculty or process of mind by which the mind generates ideas of what could be, whether these ideas accord with or conform to the laws and features of the natural world.

Beliefs rooted in the imagination which do not accord with or conform to the laws and features of the natural world are only apparently justified in the context of worlds that have been invented. Such beliefs can, however, be rooted in rules or features that are internally consistent within an invented world. For example, in the context of the invented world imagined by J.R.R. Tolkien known as Middle Earth, one is apparently justified in believing that Minas Tirith is (or at some point became) the capital of Gondor, even though Gondor and Minas Tirith both only exist in the context of an invented world.

Here, one must distinguish between products of the imagination that are publicly shared and those that are only experienced privately. It makes no sense to speak of apparently justified belief in a product of the imagination that is only experienced by the imaginer, as the imaginer can change any aspect of his or her imagined world at any time, whether or not it is consistent with the rules of logic and laws of thought or with his or her previously imagined world.

However, as with Minas Tirith, it makes sense to speak of apparently justified belief in the context of an imagined world that has been made public. Even if J.R.R. Tolkien had retracted everything he wrote in The Lord of the Rings and claimed that the events of Middle Earth actually differed greatly from those described therein, this would not change the attributes of Minas Tirith within the context of The Lord of the Rings precisely because it contains products of Tolkien’s imagination that were made public. Had he kept the idea of Minas Tirith and its attributes to himself, it would make little sense to speak of apparently justified beliefs about Minas Tirith.