Learn Spanish (Spain): Los enemigos se odian; no se ayudan. - Enemies hate each other; they do not help each other.

In Spanish, plural reflexive pronouns (nos, os, se) are also used as reciprocal pronouns to express mutual actions like "each other" or "one another". Because enemies typically hate each other rather than just themselves, context tells us that se odian is reciprocal. If you ever need to remove ambiguity, you can add el uno al otro at the end.

Why is it Los enemigos and not just Enemigos?

When making general statements about an entire class of things or people, English drops the article (Enemies hate each other). Spanish, however, almost always requires the definite article for general subjects. This is why we must say Los enemigos.

Why are the verbs odian and ayudan in the plural form?

Reciprocal actions always require two or more participants to perform the action on each other, so the verb must naturally be plural. Since we are talking about Los enemigos (they), we use the third-person plural endings for both odiar and ayudar.

In the second half, why does no go before the pronoun se?

In Spanish, negative words like no must go before the object pronoun and the conjugated verb. The pronoun se and the verb ayudan are treated as a closely tied unit, so you cannot put no between them.