are air, smell and day concreate or abstract nouns?

[haindrick]

are air, smell and day abstract or concreate nouns?

[Tdol]

Do they have a physical existence? 'Air', when we are thinking about the mixture of gases we breathe, does have a physical existence, even if invisible, so it's a concrete noun. When we talk about an 'air or romance' or something, then I'd say we're moving into the abstract territory. A day has no physical existence for me, so it's abstract.