3. Method of Agreeableness to Reason for Fixation of Belief (a Priori Method)

In Collected Papers, Peirce (1934) described third the method of agreeableness to reason (also called the a priori method) as a way to resolve doubt. In essence, we believe what appeals to reason, not letting facts get in the way. Peirce writes:

A different new method of settling opinions must be adopted, that shall not only produce an impulse to believe, but shall also decide what proposition it is which is to be believed. Systems of this sort have not usually rested upon any observed facts, at least not in any great degree. They have been chiefly adopted because their fundamental propositions seemed "agreeable to reason" (5:382).

This method is far more intellectual and respectable from the point of view of reason than either of the others [tenacity and authority] which we have noticed... But its failure has been the most manifest. It makes of inquiry something similar to the development of taste; but taste, unfortunately, is always more or less a matter of fashion... And so from this, which has been called the a priori method, we are driven, in Lord Bacon's phrase, to a true induction (5:383).

The a priori method is distinguished for its comfortable conclusions. It is the nature of the process to adopt whatever belief we are inclined to (5:386).

Peirce identified four methods of fixation of belief:

  1. Tenacity
  2. Authority
  3. Agreeableness to Reason (a Priori)
  4. Science