Charles S. Peirce
MS 188 (Robin 364, 333): Writings 3, 23-24
The irritation of doubt causes a struggle to attain a state of belief. This struggle I shall term inquiry, though it must be admitted that this is sometimes not a very apt designation.
The irritation of doubt is the only immediate motive for the struggle to attain belief. It is certainly best for us that our beliefs should be such as may truly guide our actions so as to satisfy our desires; and this reflection will make us reject any belief which does not seem to have been so formed as to insure this result. But it will only do so by creating a doubt in place of that belief. With the doubt therefore the struggle begins and with the cessation of doubt it ends. Hence, the sole object of inquiry is the settlement [ . . . ]
1. Some philosophers have imagined that to start an inquiry, it was only necessary to utter a question or set it down upon paper, and have even recommended us to begin our studies with questioning everything! But the mere putting of a proposition into the interrogative form does not stimulate the mind to any struggle after belief. There must be a real and living doubt, and without this all discussion is idle.
2. It is a very common idea that a demonstration must rest on some ultimate and absolutely indubitable propositions. These, according to one school, are first principles of a general nature; according to another are first sensations. But in point of fact an inquiry to have that completely satisfactory result called demonstration, has only to start with propositions perfectly free from all actual doubt. If the premises are not in fact doubted at all, they cannot be more satisfactory than they are.
3. Some people seem to love to argue a point after all the world is fully convinced of it. But no further advance can be made. When doubt ceases, mental action on the subject comes to an end; and if it did go on it would be without a purpose.