THE METHODS OF SCIENCE 105

and there is nothing so useful for bringing home to the mind

an important abstract truth as the presentation of a plain and

indisputable concrete example. Anything we are certain

about, because it has been proved to us by experiment, is

certain only if we know, and because we know that a thing

which has been actually proved cannot at the same time

remain unproven, and this depends again on a still more

fundamental truth which our reason recognizes the truth,

namely, that " nothing can at the same time both be and not

be " the truth known as the principle of contradiction, which

we here bring forward as the sixth conviction which must be

tacitly, if not expressly, recognized by everyone who cultivates

science. It is, at least, latent in every scientific method we

employ. Whether or not, in ultimate analysis, the validity

of this principle can be sustained, it is at least certain that

it is constantly acted on ; and this not only in the pursuit

of science, but in the judgments and actions of every-day

life.

A seventh conviction, which is latent and is acted upon in

all the methods of science, is that of the truth of such axioms

as " the whole is greater than its part," and that " things which

are equal to the same thing are equal to each other." Merely

noting this fact, which no one will care to dispute, and reserv-

ing what more we may have to say about it for a subsequent

chapter, we will pass on to the eighth conviction implied, and

at least latent in the methods of science, namely, the principle

of causation. However much the validity of this principle

may be disputed by philosophers and such disputes will be

considered later it is impossible to deny that it is practically

acted upon by those who prosecute any branch of physical

science. It is indisputable that any sudden and unexpected

change which may be detected by any scientific observer, is

at once put down as due to some cause, while he will often

do his utmost to detect what that cause may be. That no

and there is nothing so useful for bringing home to the mind

an important abstract truth as the presentation of a plain and

indisputable concrete example. Anything we are certain

about, because it has been proved to us by experiment, is

certain only if we know, and because we know that a thing

which has been actually proved cannot at the same time

remain unproven, and this depends again on a still more

fundamental truth which our reason recognizes the truth,

namely, that " nothing can at the same time both be and not

be " the truth known as the principle of contradiction, which

we here bring forward as the sixth conviction which must be

tacitly, if not expressly, recognized by everyone who cultivates

science. It is, at least, latent in every scientific method we

employ. Whether or not, in ultimate analysis, the validity

of this principle can be sustained, it is at least certain that

it is constantly acted on ; and this not only in the pursuit

of science, but in the judgments and actions of every-day

life.

A seventh conviction, which is latent and is acted upon in

all the methods of science, is that of the truth of such axioms

as " the whole is greater than its part," and that " things which

are equal to the same thing are equal to each other." Merely

noting this fact, which no one will care to dispute, and reserv-

ing what more we may have to say about it for a subsequent

chapter, we will pass on to the eighth conviction implied, and

at least latent in the methods of science, namely, the principle

of causation. However much the validity of this principle

may be disputed by philosophers and such disputes will be

considered later it is impossible to deny that it is practically

acted upon by those who prosecute any branch of physical

science. It is indisputable that any sudden and unexpected

change which may be detected by any scientific observer, is

at once put down as due to some cause, while he will often

do his utmost to detect what that cause may be. That no