Muses nine : originally there were only three, but they were later expanded to nine.

Calliope, epic poetry and eloquence; 
Euterpe, music or of lyric poetry; 
Erato, the poetry of love; 
Polyhymnia, of oratory or sacred poetry;
Clio, of history;
Melpomene, of tragedy; 
Thalia, of comedy;
Terpsichore, of choral song and dance;
Urania, of astronomy.

Plato (427?-347BC) : renowned Greek philosopher.