Ok, but why would you type Nietzsche as ILI...? If he was so vague, then it would be natural to think that he's probably not an ILI, don't you think. Yes, they have Ni and it can be abstract sometimes, but it's still blocked by Te.
You can often tell ILIs, because when they're explaining something, they will have a barrage of facts that has a hypnotic effect on the listener. They will go on and on and on explaining something, but it's usually easy to understand because theirs thoughts are very clear, and they tend to be mostly facts. I guess it's the perfect combination of ILI's Reinin dichotomies being Objectivist, Obstinate, Constructivist, Negativist, Declaring and Process, as well as Fe PoLR that make them one of the most intellectually concrete and precise types. ILIs are very very pedantic, they will often try to back up everything they say very precisely. But not every ILI is going to be smart or right, of course. They get things wrong.
Anyway, you can often tell F types from T types, by either the way they speak, or the way they write. For T types, it is often very concrete. F types are rather vague, but they're more suited toward people. Yet when F types are speaking casually with people, they sound "normal". I guess it's just that human interaction and languages tend to be vague by nature.