…it is necessary to draw a distinction between thinking and thought. A sentence printed in a book is true or false. It embodies thought, although it does no thinking. [—]
…all deliberative meditation, or thinking proper, takes the form of a dialogue. The person divides himself into two parties which endeavour to persuade each other. From this and sundry other strong reasons, it appears that all cognitive thought is of the nature of a sign or communication from an uttering mind to an interpreting mind.
http://www.commens.org/dictionary/entry/quote-existential-graphs-instrument-logical-research-0