How the order of formality sounds to me: Least formal: "opine on" (But this also sounds a bit weird compared to your other options) In between: "opine about" Most formal: "opine upon" Keep in mind, the verb "opine" is extremely rare in the English language. It is almost never spoken, and mostly only used in scholarly essays or journals, etc. I didn't even learn this verb until my last year in high school! (a college level English course).

If you replace "opine" with "speak," you might hear the difference. "Opines upon" is far too unwieldy for both common and formal speech and should be avoided. "Opines on" is the most fluid and likely used in any scenario -- formal or otherwise. "Opines about" is misleading because "opine" is a clear and strong opinion that one makes while "About" as a preposition is often used in reference to something that is hazy and unclear. As such, "opine about" would make for a poetic statement -- Mr. Hayakawa is supposed to make a clear statement, but instead gives a superficial opinion.