köken: From Middle High German denne, tenne, from Old High German denna, a variant of danne, from Proto-West Germanic *þan. Doublet of dann. The functional split between denn and dann was prescribed only by the grammarians of the 18th century. Cognate with English then and than.
Ich möchte diese Hose kaufen, denn sie gefällt mir sehr.
because (introduces a reason for that described in the previous clause) · because (introduces an explanation to a claim in the previous clause)
köken: Inherited from Old Galician-Portuguese porque, from Vulgar Latin [Term?]. By surface analysis, univerbation of por (“for”) + que (“that”). Doublet of por que. Cognate with Galician and Spanish porque, Catalan perquè, French parce que and Italian perché.
aile: porque sim
Escondi-me porque tive medo.
Naquela manhã levantara-se ainda um pouco mais lânguido que do costume, porque passara mal a noite.