My paper of November 1877, setting out from the proposition that the agitation of a question ceases when satisfaction is attained with the settlement of belief. . . goes on to consider how the conception of truth gradually develops from that principle under the action of experience, beginning with willful belief or self-mendacity, the most degraded of all mental conditions; thence arising to the imposition of beliefs by the authority of organized society; then to the idea of settlement of opinion as the result of fermentation of ideas; and finally reaching the idea of truth as overwhelmingly forced upon the mind in experiences as the effect of an independent reality.

The third philosophical stratagem for cutting off inquiry consists in maintaining that this, that, or the other element of science is basic, ultimate, independent of aught else, and utterly inexplicable – not so much from any defect in our knowing as because there is nothing beneath it to know. The only type of reasoning by which such a conclusion could possibly be reached is retroduction. Now nothing justifies a retroductive inference except its affording an explanation of the facts. It is, however, no explanation at all of a fact to pronounce it inexplicable. That, therefore, is a conclusion which no reasoning can ever justify or excuse.

Abduction consists in studying facts and devising a theory to explain them. Its only justification is that, if we are ever to understand things at all, it must be in that way.

[Scientific procedure] will at times find a high probability established by a single confimatory instance, while at others it will dismiss a thousand as almost worthless.