Full Idea
The concept of a species contains only eternal or necessary truths, whereas the concept of an individual contains, regarded as possible, what in fact exists or what is related to the existence of things and to time.
Gist of Idea
Truths about species are eternal or necessary, but individual truths concern what exists
Source
Gottfried Leibniz (Letters to Antoine Arnauld [1686], 1686.06)
Book Reference
Leibniz,Gottfried: 'The Leibniz-Arnauld Correspondence', ed/tr. Mason,HT/Parkinson,GHR [Manchester UP 1967], p.41
A Reaction
This seems to be what is behind the preference some have for kind-essences rather than individual essences. But the individual must be explained, as well as the kind. Not all tigers are identical. The two are, of course, compatible.
Related Idea
Idea 12987 For some sorts, a member of it is necessarily a member [Leibniz]