～てはいけないMust not, May not

Both "なくてはいけない" and "てはいけない" express obligation or prohibition in Japanese. "なくてはいけない" is used when the speaker must do something or something needs to be done. On the other hand, "てはいけない" is used to convey prohibition, as in the speaker must not do something or something must not be done.

Japanese grammar point "てはいけない" is generally used when conveying something that should not be done, a realization of negative rules or prohibitions. On the other hand, "なくてはならない" is used to express a strong obligation or necessity for something to be done. So, while the first implies 'must not do,' the second signifies 'must do'.

The Japanese grammar point てはいけない is used to express that something must not be done, meaning it's prohibitive. On the other hand, なければいけない is used to say that something must be done, implying an obligation or necessity. So the primary difference between the two lies in whether an action is obligatory or forbidden.

The phrase "てはいけない" is used in Japanese to express a strong prohibition, translating roughly into "must not" or "can't" in English. On the other hand, "なければならない" is used to state a necessity or obligation, meaning "must" or "have to". Therefore, the key difference revolves around whether the speaker is conveying a prohibition or an obligation.

The Japanese grammar points てはいけない and なくちゃ・なきゃ both express the idea of "must not do" or "have to do." However, てはいけない tends to be more formal and strict, often used in rules or to give warnings. On the other hand, なくちゃ・なきゃ is more casual and informal, often used in daily conversations or to express personal obligations or needs.

Both てはいけない and てはならない are Japanese expressions used to indicate a prohibition or the need to refrain from doing something. While they are mostly interchangeable, てはならない is slightly more formal and sometimes has stronger connotations. It is more likely to be seen in written rules or regulations, or in formal speeches. Conversely, てはいけない is more commonly used in ordinary conversation and everyday language.

The Japanese grammar point "てはいけない" is used to express strong prohibition, like "must not" or "should not" do something. On the other hand, "べきではない" is used to advise against doing something or to express that something "should not" be done, but with a softer nuance than "てはいけない". While both express negative recommendations, "てはいけない" is more forceful and often used in rules or laws, while "べきではない" is more of a personal opinion or advice.

The Japanese grammar point なくてもいい roughly translates to "it's okay if not," and is used to express that something is not necessary or doesn't need to be done. On the other hand, the grammar point てはいけない translates to "must not do," and is used to express that something should not or must not be done. So the main difference between the two is that なくてもいい indicates optional action, while てはいけない indicates prohibited action.

The phrase べからず is a classic, literary expression used to emphasize that something should not be done. It's rarely used in daily conversation and you're most likely to encounter it in proverbs, formal speeches, or historical manuscripts. On the other hand, てはいけない is much more common in regular speech and writing, and it is a straightforward way to state that something must not be done, often translating to "you must not" or "it's not allowed".