How convenient does it prove to be a rational animal, that knows how to find or invent a plausible pretext for whatever it has an inclination so to do.

Benjamin Franklin (1706-1790) American statesman, scientist, philosopher, aphorist

The Life of Benjamin Franklin (1791)
    (Source)

Often paraphrased: "Man is a rational animal. He can think up a reason for anything he wants to believe." Sometimes attributed to Anatole France.