This page is part of my unofficial solutions manual to the GRE Paper Practice Book (2e), a free resource available on the ETS website. They publish the questions; I explain the answers. If you haven’t worked through the Practice Book, give Section 3 a shot before reading this!

3.17: “In medieval philosophy …”

Our big clue here is the presumption of a “determinate cause” — something fixed and defined that accounts for any given phenomenon. The blank represents something that is excluded by this way of thinking, something that must be the opposite of a “determinate cause.” Possible fill-ins thus include indeterminacy (remember, you don’t need to get creative with these) and randomness.

Of the six answer choices, the only two answers that fit this set of meanings are happenstance (A) and chance (B). If you approached this question synonyms-first, you might be tempted to choose error (C) and miscalculation (F), but consider that a mistake can be predetermined rather than random. The fate of the Mars Climate Orbiter provides a case in point: the spacecraft disintegrated in the Martian atmosphere due to a unit conversion error, a mistake that was written into the ground control software.