Diogenes Laertius' book "Lives of the Philosophers" is source for many early Greek philosophers including Protagoras; but this work was compiled over six hundred years after Protagoras' death and consequently not accurate. [[Plato]] also wrote about Protagoras, considering him a sophist; [[Aristotle]] regarded Protagoras as who first introduced a spiritual principle, as a sober man among the inebriated. | Diogenes Laertius' book "Lives of the Philosophers" is source for many early Greek philosophers including Protagoras; but this work was compiled over six hundred years after Protagoras' death and consequently not accurate. [[Plato]] also wrote about Protagoras, considering him a sophist; [[Aristotle]] regarded Protagoras as who first introduced a spiritual principle, as a sober man among the inebriated. |