Full Idea
To me, there appear to be only three principles of connection between ideas, namely, Resemblance, Contiguity in time or place, and Cause or Effect.
Clarification
'Contiguity' means closeness
Gist of Idea
All ideas are connected by Resemblance, Contiguity in time or place, and Cause and Effect
Source
David Hume (Enquiry Conc Human Understanding [1748], III.19)
Book Reference
Hume,David: 'Enquiries Conc. Human Understanding, Morals', ed/tr. Selby-Bigge/Nidditch [OUP 1975], p.24