bottom of it, at the/get to the

To discover the origin of a problem, or the fundamental truth of an issue or event. The word “bottom” has been used in this way (to mean ultimate cause) since the sixteenth century. Shakespeare used it numerous times, as in “Is there no pity . . . that sees into the bottom of my grief?” (Romeo and Juliet, 3.5). Several early proverbs also refer to “bottom” in this way: “If thou canst not see the bottom, wade not”; and “He brought the bottome of the bag cleane out” (John Heywood, 1546). The pioneer anthropologist James Burnett, Lord Monboddo, wrote in 1773 (Of the Origin and Progress of Language), “In order to get to the bot- tom of this question.”