Full Idea
Substances are things that have a source of change or principle of activity within them.
Gist of Idea
Substances contain a source of change or principle of activity
Source
David Wiggins (Substance [1995], 4.4.1)
Book Reference
'Philosophy: a Guide Through the Subject', ed/tr. Grayling,A.C. [OUP 1995], p.219
A Reaction
A vey significant concession. I think we can talk of 'essences' and 'powers', and drop talk of 'substances'. 'Powers' is a much better word, because it immediately pushes the active ingredient to the forefront.