Full Idea
Which ever hypothesis be clearest and truest, ...our knowledge concerning corporeal substances, will be very little advanced.. , till we are made see, what qualities and powers of bodies have a necessary connection or repugnancy one with another.
Gist of Idea
We will only understand substance when we know the necessary connections between powers and qualities
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 4.03.16)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.548
A Reaction
A part from the emphasis on powers, this sounds a bit like Armstrong's account, that laws are the necessary connections between properties. It is scientific essentialism because Locke expects researchers to discover this stuff.