"Denn" is a coordinating conjunction approximately meaning "as a result of." It cannot be used to begin a sentence, but can begin independent clauses that are after others. This definition is the same as that of "for" when it is used as a conjunction. "Weil" is a subordinating conjunction with approximately the same meaning as "denn". It can begin a sentence, but its clause must be followed by an independent one. Words such as "nur" can be used to modify its meaning. "Because" can be used in the same way.
Are the pairs denn-for and weil-because linked somewhere in the evolution of English, or are they a coincidence?