てはいけない

てはいけない is a grammatical construction used to indicate that something is prohibited or not permitted. It is derived from the て form of a verb followed by はいけない, meaning 'it is not good' or 'it is forbidden.' This construction is prevalent in both spoken and written Japanese and is often used to give advice or warning against certain actions.

It's important to note that using てはいけない carries a strong sense of authority and is typically employed in formal situations or when instructing someone not to engage in a specific behavior. The construction can be applied to various verbs and can indicate both moral and practical prohibitions.

• It can be used among friends in casual conversation if the speaker is emphasizing an important point.
• While it conveys prohibition, it's less harsh compared to some other forms of refusal and shows concern.