Full Idea
There are necessities grounded in the individual real essences of things, and necessities grounded in the natural kind essences of things. In the first case, without the property it isn't that individual, and in the second it isn't a member of that kind.
Gist of Idea
Individual essences necessitate that individual; natural kind essences necessitate kind membership
Source
Brian Ellis (Scientific Essentialism [2001], Intro)
Book Reference
Ellis,Brian: 'Scientific Essentialism' [CUP 2007], p.11
A Reaction
This is the distinction we must hang onto to avoid a huge amount of confusion in this territory. I just say that ceasing to be that individual will presumably entail ceasing to be that kind, but not necessarily vice versa, so individual essences rule.