Various views exist concerning seasonal references, such as the necessity of a kigo insisted by the uki (kigo zettai) (absolute inclusion of seasonal reference) school, the importance of a 'kikan' (sense of the seasons) backed by the kikan school, and the tolerance of muki (no seasonal reference) by the muki school who believe that the muki haiku can create a far stronger sentiment than the traditional haiku.
季語を必ず入れなければならないとする有季（季語絶対）派から季語よりも季感が大切とする「季感」派、無季でもよいとする無季容認、無季俳句が旧来の俳句的情趣を打破するという「無季」派まで、さまざまな考え方がある。