René Descartes
Descartes considered animal as merely ‘mechanisms’ or ‘automata’——complex physical machines without experience because they can’t talk or philosophizing as human. So, they are lack of soul and thinking. Method (1637) and Meditations (1641)
Ralph Cudworth disagreement of René Descartes and his concept of soul
Animals might not speak or think like human, however they have feeling and regarding to the various animal behaviors, Cudworth claimed animals like human, have soul.
Jean-Jacques Rousseau philosophy theory of animal right
Rousseau in the Discourse on Inequality argued that animals should be part of natural law, not because they are rational but because they are sentient. He argued that sensitivity, the capacity to experience pleasure and suffering, entitles rights. Animals being sensitive experience pain and suffering and therefore as a consequence they should have rights.
Compare to human, for us it is hard to tell what is their actual feelings and consciousness. But based on the current understanding of the animals behavior, some behaviors or purposes of the animals are quite obviously recognized such as “eating”, “playing”, “hot”, “family”. However, I believe they don’t have ideas or concepts of diet, heat stroke, mental illness even though some animals might also suffer from mental illness according to the cases happening until now. On the other hand, people might ignore that animals also have their life circle and they might also have their perception or defination of things, for example they will use their language to defined “heat stroke” in their world that we will never know. Even so, they still use their language to communicate with human.
For the animals, do they realize anything happened on them, for example, if they can realize concept such as disease, over eat, mental illness?
Reference: Philosophy Now, Sydney, Kaldas (2015) Available at https://philosophynow.org/issues/108/Descartes_versus_Cudworth_On_The_Moral_Wort h_of_Animals
Grimsley. R, (1973) The phiolsophy of Rousseau, London Oxford NewYork