The problem breaks into two subordinate problems.
(1) How is the subdivision and measurement of the several sensorial spaces completely effected? and
(2) How do their mutual addition and fusion and reduction to the same scale, in a word, how does their synthesis, occur?
I think that, as in the investigation just finished, we found ourselves able to get along without invoking any data but those that pure sensibility on the one hand, and the ordinary intellectual powers of discrimination and recollection on the other, were able to yield; so here we shall emerge from our more complicated quest with the conviction that all the facts can be accounted for on the supposition that no other mental forces have been at work save those we find everywhere else in psychology: sensibility, namely, for the data; and discrimination, association, memory, and choice for the rearrangements and combinations which they undergo.