Faith Alone
I wish the reader to understand that as often as we mention Faith alone in this question, we are not thinking of a dead faith, which worketh not by love, but holding faith to be the only cause of justification. (Gal. 5:6; Rom. 3:22.) It is therefore faith alone which justifies, and yet the faith which justifies is not alone: just as it is the heat alone of the sun which warms the earth, and yet in the sun it is not alone, because it is constantly conjoined with light.
John Calvin, Tracts Relating to the Reformation, V3 (Edinburgh: Calvin Translation Society, 1851), 152.