Full Idea
Throughout the whole texture of philosophy we distinguish two modes of explanation: the analytic mode, which tends to explain wholes in terms of parts, and the synthetic mode, which explains parts in terms of the wholes or contexts in which they occur.
Gist of Idea
Analytic explanation is wholes in terms of parts; synthetic is parts in terms of wholes or contexts
Source
Nuel D. Belnap (Tonk, Plonk and Plink [1962], p.132)
Book Reference
'Philosophical Logic', ed/tr. Strawson,P.F. [OUP 1973], p.132
A Reaction
The analytic would be bottom-up, and the synthetic would be top-down. I'm inclined to combine them, and say explanation begins with a model, which can then be sliced in either direction, though the bottom looks more interesting.