The primary intension of a word or sentence is its sense, i.e., is the idea or method by which we find its referent. The primary intension of "water" might be a description, such as "watery stuff". The thing picked out by the primary intension of "water" could have been otherwise. For example, on some other world where the inhabitants take "water" to mean "watery stuff", but where the chemical make-up of watery stuff is not H2O, it is not the case that water is H2O for that world.