Paul Alexandre René Janet (French pronunciation: [pɔl alɛksɑ̃dʁ ʁəne ʒanɛ]; 30 April 1823 – 4 October 1899) was a French philosopher and writer.

In 1864 he was appointed to the chair of philosophy at the Sorbonne, and elected a member of the academy of moral and political sciences.

However, in the opinion of Encyclopædia Britannica (11th edition, 1911), these writings are not characterised by much originality of thought.

His principal work, Théorie de la morale, owes much to Immanuel Kant.

Charles Darwin was familiar with Janet's ideas, but thought that he had not well understood the theory of natural selection, as he indicated in a letter of 1866 to Alfred Russel Wallace:[1] As for M. Janet he is a metaphysician & such gentlemen are so acute that I think they often misunderstand common folk.