Silly Saturday

A few days ago my Editor came across these doodles while sorting stuff in the attic. They were done by Son#2 (who was/is an inveterate doodler) quite a number of years ago when Son#1 was at uni studying philosophy.

Can you identify the philosophers depicted? (I confess that it took me a moment to work out the middle one.)

As soon as I saw this I reckoned I'd photograph it for this month's Silly Saturday challenge, in memory of the challenge's originator Admirer and kindly hosted this month by Energia, who has sadly just lost a friend so I hope the silly blips will bring her some cheer.