Theories of Forgetting

[Ready for Fall 2026]

Modified: 2026-08-03 7:01 PM CDST

• Forgetting is important. If nothing else, it prevents us from filling our heads with useless and outdated knowledge.
  • The question of how forgetting takes place is far from resolved, however.
    • An early theory of forgetting was the decay theory. It held that older memories decayed or rotted over time. The data, however, do not support decay theory.
  • Another unresolved theoretical issue is whether forgetting really takes place.
    • Retrieval-failure theories state that memories never disappear; they just cannot be found.
    • True-forgetting theories state that some memories do disappear and that no amount of searching will ever find them.
  • Interference theories state that two kinds of interference are always operating.
    • Proactive interference works from the past to the present.
    • Retroactive interference works from the present back to the past.
    • The graphics proactive and retroactive show how one would experimentally measure both kinds of interference.
    • Most memory items are subject to both kinds of interference.
    • Think of taking two final exams on the same day and studying for them the night before.
    • Studying for the first exam will interfere proactively with your studying for the second exam.
    • Then, studying for the second exam will interfere retroactively with your memory from studying for the first exam.