The American philosopher W. V. O. Quine, in his "Two Dogmas of Empiricism", famously challenged the distinction, arguing that the two have a blurry boundary.

In modern times, philosophers have challenged the notion that human beings' status as natural beings should determine or dictate their normative being.

But one day, when an older Christian philosopher whom Justin came to revere as a second Socrates challenged his Platonist assumptions, Justin admitted that his own experience of philosophic searching forced him to a conclusion that he had long resisted: that the human mind by itself cannot grasp ultimate truth.

Leibniz, and some more recent philosophers, challenged the theory because it seems to entail that God's goodness consists of his following his own commands.

Hear philosophers, scientists, politicians, novelists, historians and artists challenge each other.