50 Philosophy Ideas You Really Need to Know

Have you ever lain awake at night fretting over how we can be sure of the reality of the external world? Perhaps we are in fact disembodied brains, floating in vats at the whim of some deranged puppet-master? If so, you are not alone - and what's more, you are in exalted company. For this question and others like it have been the stuff of philosophical rumination for centuries, from Plato to Poppe...