The Metamorphosis by Franz Kafka confronts readers with the question of whether humanity is a matter of outward form or inward spirit.
Gregor in the course of the story is inhuman in outward appearance. He also lacks the ability to speak using human language. In many other ways though, such as his interest in music and his love for his family, he retains his humanity.
The main issue in the story is not so much that Gregor himself because less human except outwardly. The narrator lets us inside Gregor's mind, which has completely human thoughts. Instead, he is dehumanized by his family, who treat him as an animal, gradually removing all external signs of humanity from him by the way they treat him, removing his things from his room and hiding him away. Although his sister tries to be kind to him, eventually his outward form and inability to communicate make it impossible for him to co-exist in human company.