C# List: why you cannot do `List foo = new List();`

Question

If you have an Interface IFoo and a class Bar : IFoo, why can you do the following:

List foo = new List();          


        

Answer 1

It is to do with the creation of the List, you have specified the T to be IFoo therefore you cannot instantiate it as a Bar since they are different types, even though Bar supports IFoo.