Thus we get a wholly new metaphysical position. Taking the elements of the traditional seventeenth-century cosmology and simply rearranging them, Berkeley shows that, if substance means that which exists in its own right and depends on itself alone, only one substance need be asserted to exist, namely, mind. Nature as it exists empirically for our everyday perception is the work or creature of mind; nature in Galileo's sense, the purely quantitative material world of the physicist, is an abstraction from this, it is so to speak the skeleton or armature of the nature we perceive through our senses, and create in perceiving it. To sum up: we first, by the operation of our mental powers, create the warm, living, coloured, flesh-and-blood natural world which we know in our everyday experience; we then, by the operation of abstractive thinking, remove the flesh and blood from it and are left with the skeleton. This skeleton is the ‘material world’ of the physicist.
In the essence of Berkeley's argument as thus restated there is no flaw. He often expressed himself hastily, and often tried to support his contentions by argument that is far from sound; but no criticism of details touches his main position, and as soon as one understands the problem which confronted him one is bound to realize that he solved it in the only possible way. His conclusion may seem unconvincing, and the difficulties in which it places us are undeniable; but there is no way of escaping the admission that, if the conceptions of mind and matter are defined as they were defined by the cosmology of the seventh century, the problem of discovering an essential link between them can only be solved as Berkeley solved it. (The Idea of Nature, 1960: 114-115)