  In general, he holds that people do not learn what they should: “Many do not understand such things as they encounter, nor do they learn by their experience, but they think they do” (B17). Indeed, they do not process the information they receive: “Having heard without comprehension they are like the deaf; this saying bears witness to them: present they are absent” (B34). Heraclitus explains: “Poor witnesses for men are the eyes and ears of those who have barbarian souls” (B107). A barbarian was a non-Greek; just as a foreigner hears Greek words without understanding their meaning, most people perceive without understanding the world around them. Sense perception is necessary for knowledge, but not sufficient; without the ability to decipher information from the senses, one cannot understand the world.