No, ‘then’ is not a preposition. In English grammar, ‘then’ is primarily used as an adverb.
It serves several purposes: it can indicate time, meaning something that happens next or subsequently, as in the sentence, ‘We went to the store, and then we had lunch.’ In this example, ‘then’ connects two actions in the order they occurred.
Additionally, ‘then’ can also be used in conditional sentences to imply a consequence, as in ‘If you finish your homework, then you can watch TV.’ Here it suggests the result of the first action.
While ‘then’ might sometimes be confused with prepositions due to its function in connecting ideas, it neither describes a relationship between a noun and another word, nor does it convey direction, location, or time in the way prepositions like ‘in’, ‘at’, or ‘on’ do. Therefore, understanding how ‘then’ operates within sentences helps clarify its role as an adverb rather than a preposition.