I know I should know what evidence is, but I have been unable to find an in-depth definition of it.

I originally thought that it was a when an argument against a theory or hypotheses was proven false, then that would be evidence for the theory or hypothesis but I haven't found anything supporting this. Please help.

  • Hi, welcome to Philosophy SE. Please visit our Help Center to see what questions we answer and how to ask. Questions about definitions of terms, even philosophical terms, are off-topic here, please consult dictionaries, Wikipedia or Stanford Encyclopedia of Philosophy.
    – Conifold
    Nov 12, 2018 at 22:20
  • When you say "falsifying argument" do you mean a "falsifiable argument"? Welcome to this SE! Nov 12, 2018 at 22:36
  • Christian philosopher William Lane Craig recently addressed a related question, "Do extraordinary claims require extraordinary evidence?" on his website. ( reasonablefaith.org/writings/question-answer/… ) He uses Bayesian ratios to explain his position, and writes: "What is really at issue is the meaning of the term 'extraordinary.'" Nov 14, 2018 at 0:11
  • I'm gonna add another question to this question, in hope to differentiate between the notions of evidence and proof: Consider a crime scene: dead body, bullet casings, blood, fingerprints. Are the fingerprints proof of guilt? Are the fingerprints evidence? Nov 14, 2018 at 6:57

2 Answers 2


To find an in-depth definition of evidence one could look at how it is described in various on-lines encyclopedias. Here are some.

Wikipedia describes evidence in the following way:

Evidence, broadly construed, is anything presented in support of an assertion. This support may be strong or weak. The strongest type of evidence is that which provides direct proof of the truth of an assertion. At the other extreme is evidence that is merely consistent with an assertion but does not rule out other, contradictory assertions, as in circumstantial evidence.

What this tells us is that an "assertion" comes first. Evidence is something that supports an assertion. Also some evidence is strong and some evidence is weak.

Let's move to the Internet Encyclopedia of Philosophy. Victor DiFate describes evidence as:

The concept of evidence is crucial to epistemology and the philosophy of science. In epistemology, evidence is often taken to be relevant to justified belief, where the latter, in turn, is typically thought to be necessary for knowledge. Arguably, then, an understanding of evidence is vital for appreciating the two dominant objects of epistemological concern, namely, knowledge and justified belief. In the philosophy of science, evidence is taken to be what confirms or refutes scientific theories, and thereby constitutes our grounds for rationally deciding between competing pictures of the world. In view of this, an understanding of evidence would be indispensable for comprehending the proper functioning of the scientific enterprise.

Here we learn that evidence is relevant to "justified belief" and "knowledge" which "epistemology" studies. Evidence can also be used to confirm or refute scientific theories. A study of evidence from the perspective of the scientific enterprise would involve the "philosophy of science".

Lastly, let's consider what the Stanford Encyclopedia of Philosophy has to say about evidence. Thomas Kelly claims there is a "tension" about what evidence means to different people::

Moreover, it is not simply that the accounts of evidence that have been advanced by philosophers stand in at least some prima facie tension with much that is said and thought about evidence outside of philosophy. As even the cursory survey offered above makes clear, philosophers themselves have offered quite divergent theories of what sorts of things are eligible to serve as evidence.

This brings us to the OP's question: What is evidence?

There is some general agreement about what evidence is based on the first two references. It is what justifies belief and provides knowledge. It is what allows us to confirm or refute scientific theories.

However, there is also tension between the different ways people use the word evidence and as Kelly further remarks, "it is far from obvious that any one thing could play all of the diverse roles that evidence has at various times been expected to play."


DiFate, V. "Evidence" Internet Encyclopedia of Philosophy https://www.iep.utm.edu/evidence/

"Evidence", Wikipedia https://en.wikipedia.org/wiki/Evidence

Kelly, Thomas, "Evidence", The Stanford Encyclopedia of Philosophy (Winter 2016 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/win2016/entries/evidence/.


Welcome to PSE. Conifold's recommendation to check out Stanford is excellent. Don't hesitate. In the meantime a brief account of the nature of evidence is the following, taken from a review of Peter Achinstein's The Book of Evidence:

Two are the main planks of Achinstein's approach. The first is that for something e to be evidence for a hypothesis H, it must be the case that the probability of H given e should be higher than 1/2. That is, prob (H/e) > 1/2. So, Achinstein does not work with a positive relevance requirement. As he shows in detail, that a piece of evidence e increases the probability of a hypothesis H does not make belief in H reasonable. Rather, he works with an absolute concept of evidence: e is evidence for H only if e is not evidence for the denial of H. This is meant to capture the view that evidence should provide a good reason for belief. He is certainly right in claiming that if scientists have a concept of evidence, it is this absolute concept. The second plank of his theory is that this absolute conception of evidence is not sufficient for reasonable belief (though it is necessary). What must be added is that there is an explanatory connection between H and e in order for e to be evidence for H. To be more precise, what is also necessary is that the probability that there is an explanatory connection between H and e, given H and the evidence e, should be more than 1/2. Call E(H/e) the claim that there is an explanatory connection between H and e. Achinstein's second plank is that prob (E(H/e)/H & e) > 1/2. Briefly put, the idea is that e is evidence (a good reason) for H only if prob(E(H/e)/e & H)>1/2 and prob(H/e)>1/2. (Actually, that's not quite accurate, as Achinstein explains in detail. What needs to be added - apart from taking e to be true and not entailing H - is that the product of these two probabilities should be greater than 1/2.) (Stathis Psillos, 'The Book of Evidence by Peter Achinstein', Philosophy and Phenomenological Research, Vol. 68, No. 3 (May, 2004), pp. 740-743: 741.)


Stathis Psillos, 'The Book of Evidence by Peter Achinstein', Philosophy and Phenomenological Research, Vol. 68, No. 3 (May, 2004), pp. 740-743.

Peter Achinstein, The Book of Evidence, Published by Oxford Univ Press (2003) ISBN 10: 0195171713 ISBN 13: 9780195171716. (Reprinted 2016.)

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