Full Idea
It sounds right to say that Fred's being a bachelor consists in (reduces to) being an unmarried male, but slightly off to say that Fred's being an unmarried male consists in (or reduces to) being a bachelor. There is a corresponding explanatory asymmetry.
Gist of Idea
'Bachelor' consists in or reduces to 'unmarried' male, but not the other way around
Source
Gideon Rosen (Metaphysical Dependence [2010], 10)
Book Reference
'Modality', ed/tr. Hale,B/Hoffman,A [OUP 2010], p.124
A Reaction
This emerging understanding of the asymmetry of the idea shows that we are not just dealing with a simple semantic identity. Our concepts are richer than our language. He adds that a ball could be blue in virtue of being cerulean.