DIFFERENTIAL: “a difference or the amount of difference, as in rate, cost, quantity, degree, or quality, between things that are comparable.” — Random House Dictionary
There is a difference between differential and difference. However, it would be inaccurate to say there is a differential between differential and difference. Are we clear?
Differential in its noun form refers to a difference in quantity — more specifically, a change in quantity. Accountants prize knowledge of “price differentials” and engineers can bandy about “bandwidth differential,” but you (and you know who you are) cannot refer to the differential between a PowerPoint deck and the handout. And if you argue that you can because presentations involve numbers, you need to go back in time to the Middle Ages, where universities taught logic instead of the semiotics of Kanye lyrics (and didn’t tolerate the kind of stream-of-consciousness word association so many substitute for reasoning today).
The word you seek is difference. There is a difference between right and wrong. There is a difference between decaf and full-test. There is even a difference between the prices of toner at your local Staples and OfficeMax. (The differential is between the rate of increase in their prices, or between one store’s prices in different markets.) Look. If you don’t know, just use the word difference. It works fine even if differential is proper, and you don’t sound like a pretentious ignoramus (or a manager) if it isn’t.
— Otto E. Mezzo