The questions of philosophy proper are human desires and fears and aspirations - human emotions - taking an intellectual form.

Science asks no questions about the ontological pedigree or a priori character of a theory, but is content to judge it by its performance; and it is thus that a knowledge of nature, having all the certainty which the senses are competent to inspire, has been attained--a knowledge which maintains a strict neutrality toward all philosophical systems and concerns itself not with the genesis or a priori grounds of ideas.

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?

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

What a fearful object a long-neglected duty gets to be

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.