Full Idea
Propositions such as 'People usually tell the truth' seem to count as default reasonable, but it is odd to count them as a priori. Empirical indefeasibility seems the obvious way to distinguish those default reasonable propositions that are a priori.
Clarification
'Indefeasible' means there are no counterexamples
Gist of Idea
Lots of propositions are default reasonable, but the a priori ones are empirically indefeasible
Source
Hartry Field (Apriority as an Evaluative Notion [2000], 1)
Book Reference
'New Essays on the A Priori', ed/tr. Boghossian,P /Peacocke,C [OUP 2000], p.120
A Reaction
Sounds reasonable, but it would mean that all the uniformities of nature would then count as a priori. 'Every physical object exerts gravity' probably has no counterexamples, but doesn't seem a priori (even if it is necessary). See Idea 9164.
Related Idea
Idea 9164 We treat basic rules as if they were indefeasible and a priori, with no interest in counter-evidence [Field,H]