“It is certainly strange that there has prevailed among men the opinion that houses, mountains, rivers, in a word, any sensitive objects, have real or natural existence other than that of being perceived by understanding” Berkeley
Berkeley first expresses concern in theological fields for Hobbes' materialism and the doctrines of free-thinkers like Toland, Collins, Shaftesbury and Mandeville. His main work “Principles of Human Knowledge: where we investigate the main causes of error, difficulty in science as also the foundation and origin of skepticism, atheism and irreligion” clearly shows the intentions of his philosophical work.
Berkeley will say that the cause of all errors is to assume that the mind can elaborate abstract ideas (such as those of “body” or “existence”) so criticizes Locke's theory of general ideas and proposes absolute nominalism: ideas are nothing but namesin such a way that any idea or representation is individual, having to be very careful when using words.
For Berkeley, we only know ideas and in addition to ideas there are only ideas in the mind that perceives them and God (who makes them perceive). To affirm that there is a material world is the consequence of allowing oneself to be carried away by the fallacies of abstraction, considering the “being” of things regardless of their “being perceived”.
Berkeley is said to be not a consistent empiricist since his philosophy can be classified as an immaterialistic metaphysics since it denies the existence of the corporeal world and asserting the existence of spiritual substances such as “God” and “soul” is in a position totally opposite to Hobbes.