"This observation might be repeated with regard to all objects of the outer world which enter into relation with us. Whether the knowledge of them be of the common-place or of a scientific order matters little. Sensation is its limit, and all objects are known to us by the sensations they produce in us, and are known to us solely in this manner. A landscape is nothing but a cluster of sensations. The outward form of a body is simply sensation; and the innermost and most delicate material structure, the last visible elements of a cell, for example, are all, in so far as we observe them with the microscope, nothing but sensation."

“I have often observed, to my regret, that a widespread prejudice exists with regard to the educability of intelligence. The familiar proverb, "When one is stupid, it is for a long time," seems to be accepted indiscriminately by teachers with a stunted critical judgement. These teacher lose interest in students with low intelligence. Their lack of sympathy and respect is illustrated by their unrestrained comments in the presence of the children: "This child will never achieve anything... He is poorly endowed... He is not intelligent at all." I have heard such rash statements too often. They are repeated daily in primary schools, nor are secondary schools exempt from the charge.”

“It seems to us that in intelligence there is a fundamental faculty, the alteration or the lack of which, is of the utmost importance for practical life. This faculty is judgment, otherwise called good sense, practical sense, initiative, the faculty of adapting one's self to circumstances. A person may be a moron or an imbecile if he is lacking in judgment; but with good judgment he can never be either. Indeed the rest of the intellectual faculties seem of little importance in comparison with judgment.”

“I believe it has required a long series of accepted observations for us to have arrived at this idea, now so natural in appearance, that the modifications produced within our nervous system are the only states of which we can have a direct consciousness; and as experimental demonstration is always limited, there can be no absolute certainty that things never happen otherwise, that we never go outside ourselves, and that neither our consciousness nor our nervous influx can exteriorise itself, shoot beyond our material organs, and travel afar in pursuit of objects in order to know or to modify them.”

“Never!" What a strong word! A few modern philosophers seem to lend their moral approval to these deplorable verdicts when they assert that an individual's intelligence is a fixed quantity, a quantity that cannot be increased. We must protest and react against this brutal pessimism. We shall attempt to prove that it is without foundation.”

“It seems to me that people of talent and of genius serve better than average examples for making us understand the laws of character, because they present more extreme traits.”

“The world is but an assembly of present, past, and possible sensations; the affair of science is to analyze and co-ordinate them by separating their accidental from their constant relations.”