Full Idea
The further a disposition is from those that can confidently be pinned on molecular structure or something comparably firm, the more our talk of it tends to depend on a vague factor of 'caeteris paribus'
Clarification
'Caeteris paribus' is the qualification 'all things being equal'
Gist of Idea
Either dispositions rest on structures, or we keep saying 'all things being equal'
Source
Willard Quine (Word and Object [1960], §46)
Book Reference
Quine,Willard: 'Word and Object' [MIT 1969], p.225
A Reaction
I approve of this. It is precisely the point of scientific essentialism, I take it. We are faced with innumerable uncertain dispositions, but once the underlying mechanisms are known, their role in nature becomes fairly precise.