Inferential Justification

Justification, according to the tripartite theory of knowledge, is the difference between merely believing something that is true, and knowing it. To have knowledge, on this account, we must have justification. How our beliefs are justified is among the central questions of epistemology.

Having justification for our beliefs is, plausibly, about having good reasons to think that they are true. For a belief to be justified, it seems, it must be inferred from another belief. This type of justification is called inferential justification. It seems that three conditions must be met for a belief to be inferentially justified.

First, there must be some other idea that supports it. This other idea need not establish what is believed with absolute certainty, but it must lend some degree of support to it, it must render the belief probable. Without a supporting idea, there can be no inferential justification.

Second, we must believe that this other idea is true. It is not enough for justification that there be another idea that supports our belief; if we thought that that other idea were false then it could not possibly help to justify our belief. Inferential justification, therefore, requires the existence of a supporting idea that is believed to be true.

Third, we must have good reason for believing that this supporting idea is true. If we irrationally believe the supporting idea, then that irrationality will transfer to the belief that we base upon it; a belief can only be as justified as are the other beliefs on which it is based. For a belief to be inferentially justified, therefore it must be based in a supporting idea that is believed to be true with justification.


When contemplating the property certainty, as with knowledge, it turns out to be very difficult to provide an uncontentious analysis. Because of its many different conceptions and dimensions, the full value of certainty is surprisingly hard to capture. To that end, below is a list of quotations to help sketch a definition of the property certainty.

“Doubt is not a pleasant condition, but certainty is absurd.”
– Voltaire

“The scientist believes in proof without certainty, the bigot in certainty without proof.”
– Ashley Montagu

“There is no such thing as absolute certainty, but there is assurance sufficient for the purposes of human life.”
– John Stuart Mill

“I believe that we do not know anything for certain, but everything probably.”
– Christiaan Huygens

“What is known for certain is dull.”
– Max Ferdinand Perutz

“To be uncertain is to be uncomfortable, but to be certain is to be ridiculous.”
– Chinese proverb

“Inquiry is fatal to certainty.”
– Will Durant

“It is the certainty that they possess the truth that makes men cruel.”
– Anatole France

“If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.”
– Ludwig Wittgenstein

“Since we can never know anything for sure, it is simply not worth searching for certainty; but it is well worth searching for truth; and we do this chiefly by searching for mistakes, so that we have to correct them.”
– Karl Popper

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