Full Idea
I suggest that Armstrong has an unfamiliar notion of analysis, as not primarily a quest for definitions, but as a quest for truth-makers.
Gist of Idea
Armstrong's analysis seeks truthmakers rather than definitions
Source
David Lewis (Armstrong on combinatorial possibility [1992], 'The demand')
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.203
A Reaction
This is not a dichotomy, I think, but a shift of emphasis. A definition will probably refer to truthmakers; a decent account of truthmakers would approximate a definition.