Firstly, just to restate the grammatical terms so we know what we're talking about: The infinitive of a verb is the "to" form of the verb (like "to go", or "to run") rather that the conjugated forms (like "he goes" or "he runs"). A gerund is the present participle of a verb (the -ing form like 'going' or 'running') used as a noun. So, if your question is just how to recognize the gerund and the infinitive, it's pretty easy to do: the gerund ends in "ing" and the infinitve starts with "to" . However, I think your question is deeper than that. If you're asking about when to use the gerund instead of the infinitive, then I the kind of sentence that I have seen to be most problematic for non-native speakers is one where you have to choose between saying something like "Would you mind turning on the light ?" or "Would you mind to turn on the light ?". In a lot of other languages, the infinitive ("... to turn on the light") would be used, but to a native English speaker that sounds strange and we would always use the gerund in this kind of sentence("...turning on the light"). So, the simple answer for this kind of sentence is to use the gerund. If that's not the kind of sentence you're asking about, please feel free to explain your question in a little more detail and I'll try to answer again

acceptional?? shenanigan??