ergo (conj.)

c. 1400, from Latin ergo "therefore, in consequence of," possibly contracted from *e rogo "from the direction of," from ex "out of" (see ex-) + noun from regere "to direct, to guide" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule"). Used in logic to introduce the conclusion of a complete and necessary syllogism.