Full Idea
Conceptions and apparitions are nothing really, but motion in some internal substance of the head.
Gist of Idea
Conceptions and apparitions are just motion in some internal substance of the head
Source
Thomas Hobbes (Human Nature [1640], Ch.VII.1)
Book Reference
'British Moralists 1650-1800 Vol. 1', ed/tr. Raphael,D.D. [Hackett 1991], p.4
A Reaction
Note that he carefully covers both thought in concepts and thought in images, and also that he is not saying that thought is the substance, but that it is a 'motion'. This strikes me as an excellent word, and I think Hobbes is right.