David Hume identifies three principles of association of ideas:
1. Resemblance — one idea naturally suggests another if they are similar.
2. Contiguity in space and time — ideas connected by proximity (e.g., a picture reminds us of the place).
3. Cause and Effect — the most important principle; when one idea is thought of, the mind immediately anticipates its usual effect.
- (A) Correct: Resemblance is a principle.
- (B) Correct: Contiguity in space and time is a principle.
- (C) Incorrect: Juxtaposition is not mentioned by Hume.
- (D) Correct: Cause and Effect is central to Hume's philosophy.
\[
\boxed{\text{Therefore, A, B, and D are correct.}}
\]