6 THE GROUNDWORK OF SCIENCE

desire to point out not only what those foundations are, but

also the tools to be used and the kind of work requisite for

their discovery and correct apprehension. The study of

psychical states being thus indispensable, it is fortunate that

the difficulty any one may find in turning the mind inwards

upon itself can soon be overcome ; for the faculties of

introspection and retrospection, like our other faculties, can

be strengthened by exercise, and all that is ordinarily needed

to perfect it is patient perseverance.

Perceptions of external and internal facts are primary

elements of science. But neither physical facts alone nor

mental facts alone will suffice for even the commencement of

science. For that, conceptions, which are the result of both,

are needed. The facts our senses make known to us are the

existences and actions of what we regard as individual

objects, while mental facts are individual states of what is

known as " the mind " : states in which we act or are acted

on. All that we thus know are real individual (or concrete)

existences and activities. But with such materials only the

intellect could do no work at all. Thoughts, of which words

are the external signs, relate not to what concerns external or

internal individual things, but each thought relates to many

things of the same kind, i.e., to " universals." Almost always

thoughts, and the words which express them, refer to and

denote what is abstract instead of concrete, and what is

universal instead of individual. The thought symbolised by

the word " triangle " does not refer to any individual, concrete

triangle, nor even to a definite kind of triangle (e.g., to an

equilateral or non-equilateral one), but refers to " triangle-in-

general " to a triangle considered as abstract and universal,

and to all triangles as members of one class of figures. It

is the same with every noun-substantive which is not a proper

name, with every adjective, and with every verb. The words

" apple," " red," " fallen," are equally applicable to every kind

desire to point out not only what those foundations are, but

also the tools to be used and the kind of work requisite for

their discovery and correct apprehension. The study of

psychical states being thus indispensable, it is fortunate that

the difficulty any one may find in turning the mind inwards

upon itself can soon be overcome ; for the faculties of

introspection and retrospection, like our other faculties, can

be strengthened by exercise, and all that is ordinarily needed

to perfect it is patient perseverance.

Perceptions of external and internal facts are primary

elements of science. But neither physical facts alone nor

mental facts alone will suffice for even the commencement of

science. For that, conceptions, which are the result of both,

are needed. The facts our senses make known to us are the

existences and actions of what we regard as individual

objects, while mental facts are individual states of what is

known as " the mind " : states in which we act or are acted

on. All that we thus know are real individual (or concrete)

existences and activities. But with such materials only the

intellect could do no work at all. Thoughts, of which words

are the external signs, relate not to what concerns external or

internal individual things, but each thought relates to many

things of the same kind, i.e., to " universals." Almost always

thoughts, and the words which express them, refer to and

denote what is abstract instead of concrete, and what is

universal instead of individual. The thought symbolised by

the word " triangle " does not refer to any individual, concrete

triangle, nor even to a definite kind of triangle (e.g., to an

equilateral or non-equilateral one), but refers to " triangle-in-

general " to a triangle considered as abstract and universal,

and to all triangles as members of one class of figures. It

is the same with every noun-substantive which is not a proper

name, with every adjective, and with every verb. The words

" apple," " red," " fallen," are equally applicable to every kind