a series of minimalistic chairs

How minimalistic can a chair be, without losing its function? If you were to strip the chair of all that is unnecessary, what would be left?

In my bachelors project I explored both the meaning of minimalism and the functions of a chair. The result was Essential – a series of minimalistic chairs. From a classic chair to a simple seat, the series addresses the different functions of a chair. Does a chair need to have a backrest to be a chair? Does it need to have legs? Or is simply a place to sit enough?