"Gaiety is a quality of ordinary men. Genius always presupposes some disorder in the machine"

In this quote, Denis Diderot suggests that gaiety, or a cheerful and easy going disposition, is a characteristic commonly discovered in common individuals. On the other hand, he argues that real genius is frequently accompanied by some sort of disorder or abnormality within the person. This might describe a mental or mental illness, or perhaps a physical condition. Diderot suggests that this disorder is what sets geniuses apart from the rest of society, enabling them to think and produce in distinct and non-traditional ways. Basically, he is saying that while gaiety might be a typical quality, it is the condition within a genius that allows them to accomplish greatness.