Categorization thus helps one to draw conclusions and to guess about how a situation is likely to evolve. - Douglas Hofstadter

At the outset, there is a concrete situation with concrete components, and thus it is perceived as something unique and cleanly separable from the rest of the world. After a while, though — perhaps a day later, perhaps a year — one runs into another situation that one finds to be similar, and a link is made.

No reference is truly direct—every reference depends on some kind of coding scheme. It's just a question of how implicit it is.

The perception of an isomorphism between two known structures is a significant advance in knowledge-and I claim that it is such perceptions of isomorphism which create meanings in the minds of people.