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I'm starting this topic with notes on Robert Audi's Epistemology: A Contemporary Introduction to the Theory of Knowledge, 3rd Edition.

Front Matter


Perception, belief, and justification

Epistemology is the theory of knowledge and justification.

Perceptions through the senses can be justification for beliefs,[1] and justified beliefs are a goal in epistemology.[2]

Justification as process, as status, and as property

Justification is a concept with several meanings that have subtle differences.

If a belief is natural to believe, if someone can believe it without being intellectually lazy, deceptive, and so on, then the belief has the property of being justified.

If a belief is justified for someone, then they are justified in believing it--that is, it is something they should believe because of the position they're in--whether they actually do believe it or not. We can call this situational or propositional justification.[3]

If someone does believe a justified belief, then we say they justifiedly believe it.[4] We can call this belief or doxastic justification. It is grounded in situational justification.[5]

If someone gives reasons for believing something, that belief is undergoing a process of justification.[6]

Perception may be our most basic source of knowledge, at least in childhood.[7]

Knowledge and justification

Knowledge of something is grounded in the same thing that justifies the belief in it. But knowledge and justified belief are different. Knowledge is justified belief that is true.[8]

Memory, introspection, and self-consciousness

Memory beliefs are justified, but we're less confident in them the less vivid the memory.

At a low level of confidence, we can take a position of non-belief toward a proposition. We can entertain, consider, and suspend judgment on it without believing or disbelieving it.

Forming memory beliefs can involve examining your own consciousness for imagery, which is a type of introspection. Knowing you are doing this is a case of self-knowledge.[9]

Reason and rational reflection

Some beliefs are based on understanding abstract concepts, such as geometry. These concepts seem to firmly justify the beliefs and seem to form a basis for knowledge.[10]


According to the commonsense view, justified belief and knowledge about general facts can be based on either generalizations from one's own perceptions or from the testimony of others or both. Of course, our own faculties are still involved in knowing through testimony, since we must perceive the testimony and store it in memory.[11]

Basic sources of belief, justification, and knowledge

Perceptual, memorial, introspective, and a priori beliefs are the basic kinds of belief. They are grounded in their sources.

The other two types of belief, inductive and testimony-based, aren't basic. Inductive beliefs are generalizations from other beliefs. Testimony can be a source for any belief, but it is at best a secondary source, since presumably the knowledge of the person giving the testimony is grounded in some other source.[12]

Three kinds of grounds of belief

There are at least three ways beliefs are grounded in a source: Causal grounding means the experience produces the belief. It goes with the question, why do you believe that? Justificational grounding means that the experience justifies the belief. It goes with the question, why should I accept that? Epistemic grounding means that the belief constitutes knowledge in virtue of the experience. It goes with the question, how do you know that?

These three often coincide, and in those cases we can simply say the belief is grounded in the source. They don't always coincide, though. A belief can be caused by a source without being justified (e.g., brain manipulation). A belief can be justified situationally even while being caused by something else that doesn't justify it (e.g., justified by testimony but caused by brain manipulation). A justificational ground may not be an epistemic ground. You can justifiedly believe something without knowing it (e.g., the belief is false).[13]

Fallibility and skepticism

Our sources of belief are fallible. How do we know they aren't likely to be mistaken? It's an important question because the security and stability of human life depends on believing we can achieve knowledge, or at least justified belief, in many areas.

We'll address questions of skepticism, but until then we'll explore how beliefs are related to their sources in various circumstances, and we'll see that these sources often do seem to lead to justified beliefs and knowledge.[14]


Part One explores and compares the basic sources of belief, justification, and knowledge.

Part Two discusses the development and structure of knowledge and justification.

Part Three discusses what justification and knowledge are and what kinds of things can be known.

Knowledge and justification are ideals to strive for. We can use sound epistemological principles to attain more knowledge, to justify the knowledge we've gained, to evaluate the claims of others, and to avoid claiming knowledge and justification when they aren't available.[15]


Audi, Robert. 2011. Epistemology: A Contemporary Introduction to the Theory of Knowledge. New York: Routledge.


  1. Audi 2011, 1
  2. Audi 2011, 2
  3. Audi 2011, 2-3
  4. Audi 2011, 2
  5. Audi 2011, 3-4
  6. Audi 2011, 2
  7. Audi 2011, 4
  8. Audi 2011, 4
  9. Audi 2011, 4
  10. Audi 2011, 5
  11. Audi 2011, 6
  12. Audi 2011, 6-7
  13. Audi 2011, 7-8
  14. Audi 2011, 8-9
  15. Audi 2011, 9-11