For philosophers, ‘substance’ often meant the fundamental stuff of which reality is made. In ordinary speech, any kind of matter — water, chocolate — is a ‘substance’ as well. But in psychiatric parlance, a ‘substance’ is always something bad. Hence ‘substance-use disorder’, which doesn’t mean reckless employment of water and chocolate, but only the exploitation of naughty compounds such as tobacco, alcohol, or drugs not manufactured by Big Pharma.