Introducing Afterthoughts and Offhand Remarks

Spanish has two common ways of introducing an afterthought, unrelated comment or offhand remark, ways that are typically translated as "by the way" or "incidentally" in English.

The expressions used are a propósito and por cierto, with the former being somewhat less casual. Here are some examples of their usage:

• Por cierto, ¿no estás descargando música ilegalmente? (By the way, are you downloading music illegally?)
• Por cierto, el libro tiene 100 páginas. (By the way, the book has 100 pages.)
• A propósito, la ciudad está a menos de 40 kilómetros de la frontera. (By the way, the city is at least 40 kilometers from the border.)
• A propósito, tenemos más de 40.000 alumnos. (Incidentally, we have more than 40,000 students.)

Note that por cierto does not mean "certainly," as you might expect. As a noun in other usages, cierto often expresses certainty.

In some contexts, a propósito can also mean "on purpose" or "deliberately." (As a noun, propósito typically means "intention" or "purpose.") When used in that way, a propósito typically comes after the verb instead of at the beginning of a sentence. Example: Determinaron que no fue a propósito. (They determined it was not done deliberately.)

A propósito de also can be a way of saying "with respect to," "concerning" or something similar. Example: Recordé una historia que Mamá me contaba a propósito de mi padre. (I remember a story Mom would tell me about my father.)