Social choice theory is a field that deals with aggregating individual interests to determine net social preference. Any form of democracy hinges crucially upon the existence of a voting system that is free and fair. However, a famous theorem of Kenneth Arrow shows, under reasonable assumptions, that no such voting system is possible! In this talk, we will give a simple proof Arrow's theorem given by Terence Tao. We will also talk about Sen's liberal paradox which also raises some fundamental questions on the underpinnings of democracy.