Jerrold Zacharias, one of the leaders in the science education reform of the 60s and 70s, used to hand out a card with a list of "heuristic ploys" for thinking.

Assorted Heuristic Ploys

  1. Observation, evidence, and basis for belief.
  2. Order of magnitude of significant and relevant quantities; measurement.
  3. Successive approximation; exploitation of error; feedback and control of iterative processes.
  4. Reductio ad absurdum; pushing to a limit.
  5. Plurality of approaches.
  6. Mistrust of the principle of exclusion, or exhaustion.
    7. What, if not?
  7. Intellectual elegance; intellectual efficiency; taste, style, and judgment.
  8. Symmetry and invariance.
  9. Necessary and/but not sufficient conditions.
  10. Continuity and discontinuity; particulateness and quantization; interpolation; extrapolation.
  11. Analogy -- Contrast.
  12. Inference; implication and test of conjecture; verifiability, insolvability.
  13. Uniqueness, stability, conservation.
  14. Equivalence, congruence, identity.
  15. Point of view, change of scale, frame of reference.
  16. Signal to noise ratio; minor and major fluctuations.
  17. Arbitrary rules of the game.
  18. Crossterms and interactions.
  19. Anthropomorphism concerning the inanimate.
  20. Ask a friend.
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