pero

Pero is the most common adversative conjunction in Spanish, used to introduce a contrasting idea that does not negate the first clause. It functions similarly to English "but" and can join clauses of any length and register.

The key pitfall is confusing pero with sino, which is used after a negative clause to introduce a correction or replacement. "No es azul pero verde" is wrong - the correct form is "No es azul sino verde" (It is not blue but green). Use pero when the first clause is affirmative or when you are adding a contrasting observation rather than correcting a falsehood.