The process of discovery is hands-on, learning by doing. You don't know all the rules at the outset, or all the definitions, or even know what you don't know. You find out as you go along. Thus it has been for every great invention from sex to agriculture to post-it notes to landing a man on the Moon and back to on-demand porn.
The real requirement is that we have some way to test it; that we can do, e.g. by conversation. To cop an example from quantum mechanics (which I know nothing about), we don't have to understand why it is like that in order to make predictions with it.
We don't need a clear and unambiguous definition of intelligence in order to tell that other human beings are intelligent. Likewise, we don't need one in order to start trying to create an artifice that impresses us into thinking it also is intelligent.
This was quite impressive, and on the right track, seemingly: http://hci.stanford.edu/~winograd/shrdlu/