I've noticed that many famous European paintings show philosophers such as Plato, Socrates, Aristotle, etc. gesturing with one finger pointed in the air. This is probably most famously shown in Raphael's School of Athens (Plato is in the center, finger in air) and Jacques-Louis David's Death of Socrates. Does this have any historical significance, and if so, what does the gesture symbolize?
I must preface this with the fact that I'm not a historian, and therefore if this comment gets deleted I'll understand completely.
I believe the traditional interpretation of the hand gestures in the School of Athens is that Plato's finger refers to his philosophy of Idealism, the philosophy that there exist "Forms" outside of perceivable reality, which are, in a certain way, higher truths that can only be realized by the philosopher. The "Allegory of the Cave" is the classic text that illustrates Plato's ideas very succinctly.
Contrarily, Aristotle, waving downward, was more concerned with the realm of physical reality, and the gestures that the philosophers make can therefore be seen as an illustration of their opposed philosophies on ontology.