The prepositions
para and
por, from the variety of their meanings and usage, deserve a chapter to themselves. They are employed in senses that have so great an apparent resemblance, that no small care is required to distinguish them. Stated roughly,
por refers to source and
para to destination.
Example 1 Esta carta fue escrita por el general para el rey. This letter was written by the general [intended] for the king.
Of the two, por represents the most difficulty. It may be regarded as taking the places of the Latin per and pro.
Per was used in expressing the time or place "through" which anything passed; the person "through" or "by" whom, or that "on account of" which, anything was done.
The primary meaning of pro was "before", "in front of". But one might stand before another as a defender, advocate, friend or representative, and thus act or speak "for" or "on behalf of" him, or "for" his benefit; it also signified the taking, exchanging or substituting one person or thing "for" another.
These various senses are combined in the Spanish por.
Para is a combination of pro in the sense of "before", "forward", and ad, "to", so that its primary signification is "forward unto". In all its uses its characteristics are purpose, object, end or intention.