How to Say "by right" in Spanish
The Spanish word for “by right” is “legalmente” — B1 level. This is a very common word in everyday Spanish.

Examples
La empresa está legalmente obligada a pagar las horas extra.
The company is legally required to pay overtime.
Para conducir, debes obtener tu licencia legalmente.
To drive, you must obtain your license legally.
Legalmente, no pueden despedirte sin una causa justificada.
Legally, they cannot fire you without a justified reason.
Adverb Formation
Adverbs ending in '-mente' are built from the feminine form of an adjective (like 'legal' which is the same for masculine and feminine) plus the suffix '-mente'. This works just like adding '-ly' in English.
Using the Adjective Instead
Mistake: “Using 'legal' when you need 'legalmente' (e.g., *'Lo hizo legal'*).”
Correction: Always use the full '-mente' form when describing how an action (a verb) is performed: 'Lo hizo legalmente' (He did it legally).
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