The accidental causes of science are only accidents relatively to the intelligence of a man.

Natural Selection never made it come to pass, as a habit of nature, that an unsupported stone should move downwards rather than upwards. It applies to no part of inorganic nature, and is very limited even in the phenomena of organic life.

By what criterion... can we distinguish among the numberless effects, that are also causes, and among the causes that may, for aught we can know, be also effects, - how can we distinguish which are the means and which are the ends?

A fact is a proposition of which the verification by an appeal to the primary sources of our knowledge or to experience is directand simple. A theory, on the other hand, if true, has all the characteristics of a fact except that its verification is possible only by indirect, remote, and difficult means.

Let one persuade many, and he becomes confirmed and convinced, and cares for no better evidence.

The accidental causes of science are only accidents relatively to the intelligence of a man.

We receive the truths of science by compulsion. Nothing but ignorance is able to resist them.