My Evidentialist Epistemology

by Max Andrews

I would consider my epistemic position to be a moderate evidentialist. (This is just a brief outline).  There is a sense of deontology to it in that one ought to base their beliefs corresponding to the evidence; however, there is a sense in which one may hold a belief without sufficient evidence and still be rational.  The source of truth is the objective prime reality and our knowledge should correspond to the truth of reality.  My epistemology yields my theology in the sense of scientific theology.  What I know about reality is what I know about God.[1]

Everything that we know is intuitive or experiential.  Intuition will be discussed later but the knowledge gained is from sensory apparatus’.  The characters read on paper are only the result of photons reflecting off of the paper and the photoreceptors in the eye receiving that information.  All knowledge cannot be deemed sensory only since it seems feasible that a person with a sensory handicap or no functioning sensory apparatus’ may still be justified in believing in his own existence by intuition (as well as moral truths).  The task of justification, or determining the truth of p, must meet the criteria of an inference to the best explanation (IBE).

Consider the following definition for justification:

            S is justified in believing p = S possesses sufficient evidence for p to be true. 

There needs to be clarification in all the terms being used.  Possesses may seem ambiguous.  By possesses I mean that S has already gained accesses to the evidence.  It does not mean that the evidence is merely available to him since evidence for many propositions are available but S has not accessed or considered all the evidence for each available proposition that may be formed.  If possession merely meant access to sufficient evidence then S may be justified in believing almost anything.

Consider Lewis’ belief that a family of bears lives in his backyard.  How might Lewis justify himself?  Well, if merely having access to sufficient evidence is justification then he may already be justified in his belief.  This also creates a problem similar to the Gettier problem.  Suppose Lewis has never seen a bear, bear tracks, or any other evidence suggesting that a family of bears lives in his backyard.  Now suppose that there actually is a family of bears in his backyard.  Despite Lewis’ inquiry of the evidence for his belief that a family of bears lives in his backyard he would be justified in believing it.

The converse is just as absurd.  Suppose that Lewis still has not made any inquiry of the evidence for his belief.  It turns out that there actually is not a family of bears in his backyard.  Lewis could still be justified in his belief even though his belief does not correspond to reality and is false.[2]

The criteria to determine the best explanation are 1) explanatory power, 2) explanatory scope, and 3) the conclusion or belief must be more plausible than its negation.  Consider Lewis’ bear problem.  Suppose Lewis sees, what appear to be, a mother bear and three small cubs one afternoon in his backyard.  The next day he sees traces of the bears in his back yard.  This pattern continues throughout the season, which seems to indicate that the bears inhabit a nearby location.  To determine the explanatory power of p, that a family of bears lives in the backyard, p must be a robust entailment of the data.  It must correspond well to the data.  For p to meet explanatory scope p must be able to explain the greatest amount of the data over the competing hypotheses.  Given all the data and background knowledge, p must then be more plausible than ~p.  Additionally, the subjective experience of seeing a bear would be sufficient evidence to believe, at the moment, that a bear is appearing to the subject in the absence of any defeaters.

The process of constituting sufficiency is the most technical step in my opinion.  There is a certain amount of probability and background knowledge to assess sufficiency.  The belief in question is assessed as the consequent and then considering what may be the best explanation for that belief, antecedently.  This may seem fallacious but IBE is acceptable abductive reasoning.  Additionally, this abductive process only comes into the process when assessing whether the evidence sufficiently corresponds to the belief since the belief typically arises by the antecedent evidence and then as the consequent, it is the assessment of the belief that requires working backwards.

It is paramount to explicate from the beginning that this is philosophy of science and the question of ethics will be theological.  The beliefs, theories and explanatory hypotheses must lay in empirical harms way.  The conclusions must be falsifiable.  It should be noted that the type of scientific inquiry will be that of an Augustinian science as opposed to a Duhemian science.  Augustinian science permits and carries open metaphysical presuppositions with science.  Duhemian science strips science of all metaphysical imports.  This is important since this epistemic process does not restrict explanations to natural explanations in its methodology.  Persons, processes, and even unknown agents may be sufficient explanations and conclusions to the evidence. This is not as controversial as much as the scientific and philosophical community makes it out to be.  Agency is publically accepted evidence by experience and may serve as antecedent evidence as well as a consequent belief.[3]

Such methods are derived from the use of abductive reasoning.  The American philosopher and logician Charles Sanders Peirce first described abduction.  He noted that, unlike inductive reasoning, in which a universal law or principle is established from repeated observations of the same phenomena, and unlike deductive reasoning, in which a particular fact is deduced by applying a general law to another particular fact or case, abductive reasoning infers unseen facts, events, or causes in the past from clues or facts in the present.[4] Consider the following syllogism:

  1. If it rains, the streets will get wet.
  2. The streets are wet.
  3. Therefore, it rained.

The use of abductive reasoning may seem fallacious at first take.  This syllogism commits the fallacy of affirming the consequent.  One cannot deduce from the data, that the streets are wet, that it rained because there are many other explanations for why the streets are wet.  It could have been the case that a fire hydrant was allowed to flow, a street cleaner came through, a concerned citizen who wanted to clean the chalk off of the streets from the little children drawing pictures or writing words, there are many possibilities that could explain why the road was wet.  This was the problem that posed Peirce:  How was it that despite the logical problem of affirming the consequent, one nevertheless frequently makes conclusive inferences about the past?  The key point is the explanatory scope and power of the explanation.  Abductive reasoning does not derive a certain conclusion (for one would then be guilty of affirming the consequent), but it makes an inference to the best explanation.  Peirce’s example was whether anyone should believe in the existence of Napoleon.  He claimed that the past may be inferred from the study of present effects, namely, artifacts and records.  Peirce concluded, “Though we have not seen the man [Napoleon], yet we cannot explain what we have seen without the hypothesis of his existence.”[5]  Despite the apparent fallacy, W.P. Alston, W.B. Gallie, and Michael Scriven have observed, such arguments can be restated in a logically acceptable form if it can be shown that Y has only one cause (i.e. X) or that X is a necessary condition (or cause) of Y.  Thus, arguments of the form:

  1. X is antecedently necessary to Y,
  2. Y exists,
  3. Therefore, X existed

are logically valid by philosophers and persuasive by historical and forensic scientists.[6]

The suggestion was that a particular abductive hypothesis can be firmly established if it can be shown that it represents the best or only explanation of the “manifest effects” in question.[7]  The only causally adequate explanation of Lewis believing a family of bears lives in his back yard is if he has sensory evidence (since intuition may not be sufficient in this scenario).

The question of sufficiency may also be expressed probabilistically.  If my belief p is sufficient then it must be 0 < p ≤ 1 where p is > .5.  Expressing the value of p is difficult and may certainly have values that may be measured and compared but there are also instances where p must be assigned an arbitrary value that must be determined intuitively or against the aggregate whole of one’s current knowledge [if p is novel].  Additionally, if p is not equivalent to 1 then all future tensed propositions may only be expressed probabilistically.

Why these criteria for determining the value of p?  There may be instances when p may be assigned a definitive value.  Suppose that I am colorblind, to an extent, and red and purple are indistinguishable for me and that they are the same shade.  Suppose I have three marbles in my pocket that are similar in weight and texture (or otherwise may only be distinguished by color) and I have been told by a reliable source that there is one red marble and two purple marbles.  The probability of me pulling out the red marble is .333.  I pull out a marble and it is red.  Let p be the belief that I pulled a purple marble from my pocket.  With the background knowledge, k, that I have the inability to differentiate red from purple; I am justified in assigning a value of .333 to p even though I actually pulled out a red marble.  Would I then be justified? –No, because p is not > .5.  Suppose that I actually pulled out a purple marble, would p then be justified? –No, because I cannot simply ignore k.  I would then need more evidence of p based on testimony from a reliable source.[8]  My reliable source informs me that the marble is purple.  This new information, E2, must then be considered as evidence for [or against] p with my previous evidence, E1 (the probability, .333).  I now have a value for p’s sufficiency that looks like 0 < p ≤ 1 where p is (E1 + E2 | k) > .5.  E2 must have a minimum value of .168 for it to be greater than .5.  If this is the case and p has such a value then I have sufficient evidence for p that can be determined by set values (Bayesian probability would be sufficient as well).

Suppose that after all the evidence that is available is possessed and I have come to a value of precisely .5 for p.  If I reject p as being true then I have just as much of a chance of being wrong about that as I do as being right.  When p has a value of .5, all things considered, then I believe it would be acceptable to be believe p, ~p, or to be agnostic since there is no other evidence to say otherwise until more evidence is possessed.

[1] I am not suggesting that a pantheistic of panentheistic model.  I am asserting that my epistemology makes certain entailments to my theology.  I will provide a historical development of this.

[2] This may actually seem like it would be the case that Lewis is not justified assuming that knowledge is a justified true belief.  Since the bears do not actually live in his backyard it is not true.  What needs to be considered is whether or not Lewis has access to sufficient evidence that may still suggest that bears live in his back yard.

[3] For example, a person’s testimony or experience that is not of my own is acceptable evidence to consider.


[4] In the words of Stephen C. Meyer, Signature in the Cell (New York:  Harper Collins, 2009), 153.  Charles Peirce, Collected Papers, 2:375; “Abduction and Induction.”

            [5] Peirce, Collected Papers, 2:375.


[6] Stephen C. Meyer, “A Scientific History—and Philosophical Defense—of the Theory of Intelligent Design.” W. P. Alston, “The Place of the Explanation of Particular Facts in Science,” Philosophy of Science 38 (1971):  13-34.  W. B. Gallie, “Explanations in History and the Genetic Sciences” in Theories of History:  Readings from Classical and Contemporary Sources (Glencoe, IL: Free Press, 1959), 386-402. Michael Scriven, “Explanation and Prediction in Evolutionary Theory,” Science 130 (1959):  477-482.

            [7] Meyer, Signature in the Cell, 154.


[8] There is a doxastic element to my theory and the criteria for reliability would require the same criteria for sufficient evidence for it to be reliable.

7 Responses to “My Evidentialist Epistemology”

  1. Hi Max,

    Nice post. I think that the evidentialist view you sketch provides a useful perspective on most issues in applied epistemology, but I wonder if the view really could be the right approach to justification. Notice that justification is supposed to be determined by evidence possessed, not just the evidence that’s ‘out there’. So, the evidentialist needs an account of possession of evidence. It’s here that I think they run into trouble. What’s the possession relation? The view that I’ve come to accept (but resisted for years) is Williamson’s view, the view that to have p as part of your evidence just is for you to know p. If that’s the right view of possession, then it looks like we need to invoke normative notions like knowledge and justification to explicate the notion of possessed evidence. Thus, it doesn’t look like we can use the notion of possessed evidence to explicate the concept of justification.

    The evidentialist account might be a good start for understanding inferential justification, but I have real reservations about the account’s treatment of non-inferentially justified belief. It needs to give an account of possession according to which p can be possessed as evidence without assuming that p is justifiably believed (or known) and I just don’t think there’s any good non-normative story to tell about possession.

    Does that worry make sense?

    • I’m not quite familiar with this idea of “possession,” to be honest.

      Concerning non-inferentially justified beliefs you may find my paper here interesting: “Epistemological-Scientific Realism and the Onto-Relationship of Inferentially Justified and Non-Inferentially Justified Beliefs”

  2. How does your position differ from the presuppostional apologetics, are they limitations.

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