An interesting property is that when you have left and right application, which part of fx is the function and which is the argument becomes sort of ambiguous.

An interesting property is that when you have left and right application, which part of fx is the function and which is the argument becomes sort of ambiguous. You can think of f as something that combines with a B on its right to produce an A, (A/B)B = A. But you can also think of x as something that combines with an A/B on its left to produce an A, (A/B)((A/B)\A) = A. This is famously used in interpreting the status of "Socrates is mortal" ("Socrates" is the argument) and "Every man is mortal" ("is mortal" is the argument).