Full Idea
A cause it the sum or aggregate of all such accidents, both in the agents and in the patient, as concur to the producing of the effect propounded; all of which existing together, ti cannot be understood but that the effect existenth without them.
Gist of Idea
A cause is the complete sum of the features which necessitate the effect
Source
Thomas Hobbes (De Corpore (Elements, First Section) [1655], 1.6.10)
Book Reference
Hobbes,Thomas: 'Metaphysical Writings', ed/tr. Calkins,Mary Whiton [Open Court 1905], p.28
A Reaction
For most causes we meet, this definition will include gravity and electro-magnetism, so it doesn't help in narrowing things down. Notice that he accepts the necessity, despite his committed empiricism.