The generic use of alan picks out ANY REPRESENTATIVE MEMBER OF THE CLASS.
Thus any can be substituted for alan in examples like:
The best way to learn a language is to live among its speakers.
"any" sometimes has a similar but more emphatic meaning.
The greatest threat to any actor is the presumption that knowledge can be automatically transposed into experience.
You can not use this pattern when you want to talk about the location or existence of a type of animal,thing or person. For example, you can not say "A ring-tailed lemur lives in Madagascar"; you would have to say "Ring-tailed lemusr live in Madagascar" or "The ring-tailed lemur lives in Madagascar".
This use is common in explanations of meanings and in some dictionary definitions.
A mountain is bigger and higher than a hill.
In Grammar, a noun is a word which is used to refer to a person, a thing, or an abstract idea.
Grammatically,"A tiger is a strong animal " may fit the generic sense at the sentence level, but it does sound odd on its own.
Eventually, the context tells it all---not grammar rules alone.