Step 1: Hydroxide (or other base) removes the α-H of one carbonyl → enolate. - Step 2: Enolate attacks the C=O of another carbonyl → tetrahedral alkoxide. - Step 3: Protonation of alkoxide → β-hydroxy carbonyl. - Step 4 (condensation): Base removes α-H between the new C=O and the β-OH; water leaves;