Reason/ˈriːzn/ Definition 1 of 4Pro Tip 1/3Common Triggers Often used after words like 'The,' 'A,' or 'One' to introduce the cause. One reason he succeeded was his dedication. Pro Tip 2/3Question Responses Use 'reason' to answer 'Why' questions for clear explanations. The reason I study is to learn new things. Pro Tip 3/3Not Always Rational Sometimes people say 'for some reason' when a reason isn't clear or logical. For some reason, I felt anxious.