siquidem

Siquidem is si plus quidem, and the manuscripts write it both joined and apart. It takes the indicative.

The range runs from a genuine condition, "if indeed", to a flat causal, "since, seeing that", and nothing in the word itself tells you which. The test is the clause: if it states something the writer plainly accepts as fact, translate causally. Medieval prose leans almost entirely on the causal use, often no stronger than "for", and treating every siquidem as a condition will tie a straightforward paragraph into knots.