in consequence of that; as a result; consequently: I think; therefore I am.
Origin: 1125–75;Middle Englishther(e)fore, variant of therfortherefor
Can be confused: therefor, therefore (see synonym study at the current entry).
Synonyms hence, whence. Therefore, wherefore, accordingly, consequently, so, then all introduce a statement resulting from, or caused by, what immediately precedes. Therefore (for this or that reason) and wherefore (for which reason) imply exactness of reasoning; they are especially used in logic, law, mathematics, etc., and in a formal style of speaking or writing. Accordingly (in conformity with the preceding) and consequently (as a result, or sequence, or effect of the preceding), although also somewhat formal, occur mainly in less technical contexts. So (because the preceding is true or this being the case) and then (since the preceding is true) are informal or conversational in tone.
O.E. þærfore; from there + fore, O.E. and M.E. collateral form of for. Since c.1800, therefor has been used in sense of "for that, by reason of that;" and therefore in sense of "in consequence of that."