Why is Aluminium oxide amphoteric?

I was reading my book, in which it mentioned that aluminium and gallium oxides are amphoteric and and Indium and thalium oxide are basic in their properties. But no explanation was given.

Edit: My main question is we know that mostly metal oxides are basic and non metal oxides are acidic. But we see some metal being amphoteric, what is the cause of this difference ?

I tired to search online but found no reliable piece to read.

• If anyone can suggest better tags, please do thanks – DevUt Nov 28 '19 at 4:36
• These are fundamental questions. I am afraid nobody knows yet. By that I mean that science has not progressed enough to predict from $ab$ $initio$ calculations that an element with this number of neutron, protons, and electrons will have an amphoteric oxide. Yes one can predict from periodic trends like Mendeleev, but what is the fundamental cause? It is an open question I guess. – M. Farooq Nov 28 '19 at 4:46
• I suggest you first find out what exactly "amphoteric" means, and then look for examples. Why is sodium oxide basic, why do nitrogen oxides react acidic, etc. You know, start with the simpler cases. Then look for reactions that show how Al oxide can do both. – Karl Nov 28 '19 at 6:33
• @M.Farooq We can certainly predict the stability of different Al (hydr)oxides/ions. "Why" questions have a tendency to become philosophic, which is why chemists prefer to ask "how". – Karl Nov 28 '19 at 6:41