In this final post on the basic four methods of proof (but perhaps not our last post on proof methods), we consider the proof by induction. Proving Statements About All Natural Numbers Induction comes in many flavors, but the goal never changes. We use induction when we want to prove something is true about all natural numbers. These statements will look something like this: For all natural numbers n, $ 1 + 2 + \dots + n = n(n+1)/2$.