What is the Law of Identity?
The Law of identity states that if A and B are identical, that is to say they are the same thing, not two different things, then anything that’s true of A is true of B. This means that if we can show that there is something true of A that’s not true of B then A and B aren’t the same thing.
For example if John and Joe are the same person then anything that’s true about John must also be true about Joe . So if john is a male then Joe must be a male. If Joe is a physics major then John must be a physics major etc. If we can show that there something true of John, that’s not true of Joe then John and Joe aren’t the same person.
Whooo. That might have been a little confusing. Let go more into detail.
This law can be applied to the Mind and Body. For the sake of this argument let’s use mind and brain. One quick difference we might notice is that my mind or my consciousness is nonphysical, while on the other hand my brain is a chunk of physical matter. My mental states are comprised of thoughts, beliefs, desire, intentions, but matter alone has no beliefs no desires or intentions. The snow didn't intend to slide down the mountain in an avalanche and kill someone. Similarly your cells don’t desire to reproduce in order for you to live. Only a mind has intentionality, thoughts, beliefs and desires. Furthermore, mental states don’t occupy space like your brain or your body, you can’t think so hard that you fill the room with thoughts, so that no one else can think in that room. On the other hand you can fill a room with so many bodies that there isn't room for any more people. These differences along with many others have led some philosophers to conclude that the mind and mental states cannot be reduced to being purely physical brain states or the brain itself.
Other arguments can be constructed alongside this one in order to show that the mind and the body are different, such as the argument from consciousness, and the argument from intentionality.
