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Psychological Determinism is the claim that human actions are determined by psychological laws, in particular the Law of Strongest Motive.

Table of Contents

1. Psychological Determinism
2. Reid’s Classic Refutation

Psychological Determinism

• Psychological Determinism is the view that human action is determined by psychological laws, in particular the Law of Strongest Motive (LSM):
  • A person always acts according to their strongest motive.

Reid’s Classic Refutation

• The Scottish philosopher Thomas Reid set forth the classic criticism of LSM in the 18th century.
  • To find out whether LSM is true, Reid said, there must be a criterion for determining the comparative strength of motives:
    • “How shall we know whether the strongest motive always prevails, if we know not which is strongest? There must be some test by which their strength is to be tried, some balance in which they may be weighed; otherwise, to say that the strongest motive always prevails, is to speak without any meaning.”
  • The criterion cannot simply be that the motive that prevails is the strongest.
    • “Either we measure the strength of motives merely by their prevalence, or by some other standard distinct from their prevalence. If we measure their strength merely by their prevalence, and by the strongest motive mean only the motive that prevails, it will be true indeed that the strongest motive prevails; but the proposition will be identical, and mean no more than that the strongest motive is the strongest motive. From this surely no conclusion can be drawn.”
  • Reid considered two criteria:
    • That a motive is stronger than another if it feels stronger or is more intense.  
    • That a motive is stronger than another if acting on it is more rational.
  • Both criteria fail because people sometimes choose intense short-term pleasure over long-term good and other times they choose the reverse.