If a human is raised in complete isolation and ignorance, it will not be 'human' in that sense of the word.
The human mind can only develop certain skills and abilities at certain points, and then it will never be able to learn. If language is not learned by a certain point in life, the human in question will never be able to have the capacity to understand language.
However, due to the rarity of finding such children, as well as them lacking the capacity to communicate, it is impossible to determine if they have the capacity to develop and understand morals, or if they know what death is, and what they think of it.
However, the mind retains its impressionability. There was on instance in eastern Europe (I cannot recall where specifically) where are mother threw an unwanted child into a dog kennel. The child survived, but was luckily found before she was unable to learn communication. She can speak, but very poorly. Either way, she acted as dogs did, she 'barked' at threats, sniffed other dogs, slept with them, like them, howled, and otherwise acted like a dog would. It took an incredibly long time to break her of this, and even then she occasionally relapses.
If you took a cat, and raised it with and as dogs, would the same thing happen? What about a monkey?
There are so many levels to determining sapience it is impossible to determine.