Are There Limits to Cognition? 125meant by the word are not necessary to have percepts of
soul or spirit. One could object that such an extension of
normal linguistic usage is illegitimate. But it isabsolutely
necessary unless we want our cognitive growth in certain
areas to be held in chains by linguistic custom. Anyone
who speaks of perceptiononly as sense perception will
not arrive at a concept appropriate for knowledge—even
knowledge of this same sense perception. Sometimes we
must extend a concept so that it can have an appropriate
meaning in a narrower field. Sometimes, too, we must
add something to what a concept initially calls to mind so
that what is thought of initially can be justified or adjust-
ed. Thus, on page 100 of this book we read that “A mental
picture, then, is an individualized concept.” I have heard
the objection that this is an unusual use of words. But if
we are to understand what a mental picture really is, this
usage is necessary. What would become of the progress
of knowledge, if everyone who has to adjust concepts
meets with the objection, “That is an unusual use of
words”?