One example of a philosopher who believes that there is only one substance is Berkeley who argued that only the mind exists. Berkeley believed that the world is based on ideas. Although we believe that the world exists and that we have experiences of it he argued that these experiences are simply ideas supplied by God’s mind. Berkeley argued that it is only our mind, everyone else’s and God’s that exists and that we are all part of God’s ideas of the world. We interact and feel as though we are part of a physical world however there is no physical world-only God’s ideas represented as a “world”. It is simply God’s knowledge which is the foundation of our shared reality and why we can interact with each other. It is God’s knowledge which provides us with the world. Something cannot exist which is not based on God’s knowledge and ideas. The body is not a real substance as it is only an idea in God’s and human’s minds. This therefore means that Berkeley believes in a life after death, as he understands the soul to be a part of the mind. This means that at death we simply return to God’s mind as that is all we are-mind. There is no body to be left behind. Our “body” is not a real body it is only an idea of a body so this means that the mind and body are technically only mind.
Berkeley was a monist and immaterialist who believed that we were simply mental beings. Berkeley stated that we do not have a body, but instead an idea of one. He rejected ideas of a physical world, believing that there was no independent physical reality as the physical world was just an illusion. He argued that we cannot know whether there is anything beyond our sensations, and that it isn’t just God projecting sensations into our minds. Berkeley believed in philosophical idealism; the view that matter does not exist in its own right; it was just a product of the mind. In his opinion, all objects are mental creations, and since the world is a sum of all objects even the world was a mental construct. Berkeley summoned his theory through the Latin phrase ‘esse est percipi’, to be is to be perceived, which demonstrates his view that if an idea is not in our mind (or God's) then it does not exist. All of our passions, ideas and thoughts exist through the mind. He was convinced that there was an afterlife. He stated that we all have an eternal soul, and go to heaven as over time our ideas develop, becoming closer to God’s.