The diversity effect during category-based induction (CBI) means that the more diverse the evidence, the higher will be the conclusion's inductive strength. However, it is influenced by the premise typicality. Three competitive cognitive processing models account for this influence: (1) The pre-emptive conflict resolution model assumes that only premise typicality activates; (2) the parallel-competitive model assumes that premise typicality and diversity activate in parallel; and (3) the default-interventionist model assumes that a default response of premise diversity first activates and is subsequently followed by premise typicality, or premise typicality activates first, followed by premise diversity. The timing of premise typicality affecting the diversity effect during CBI was measured using event-related potentials to determine which cognitive model best explains this influence. Similar to previous studies, non-diverse premise inductive tasks involving two typical premise categories were compared with diverse premise inductive tasks involving a typical and an atypical category. The results showed that non-diverse conditions had higher “correct” response proportions, greater inductive strength, higher “definitely” response proportions, and shorter reaction times than diverse conditions, showing that premise typicality weakens the diversity effect. Moreover, the diverse premises elicited larger P2, smaller FN400, and greater frontal post-N400-positivity amplitudes than non-diverse premises, suggesting that premise diversity was facilitated during a relatively early time window and revised by premise typicality in a later window. These results support the default-interventionist in nature during thinking and reasoning.