Full Idea
The alleged naked, or rather hidden, substance of wax is something that we can neither ourselves conceive nor explain to others.
Gist of Idea
Substance cannot be conceived or explained to others
Source
comment on René Descartes (Meditations [1641], §2.31) by Pierre Gassendi - Objections to 'Meditations' (Fifth) 273
Book Reference
Descartes,René: 'Meditations on First Philosophy etc.', ed/tr. Cottingham,John [CUP 1986], p.77