Berkeley, God, ideas and other minds

In his Treatise Concerning the Principles of Human Knowledge Berkeley stated:

Whatever power I may have over my own thoughts, I find the ideas actually perceived by Sense have not a like dependence on my will. When in broad daylight I open my eyes, it is not in my power to choose whether I shall see or no, or to determine what particular objects shall present themselves to my view; and so likewise as to the hearing and other senses; the ideas imprinted on them are not creatures of my will. There is therefore some other Will or Spirit that produces them.

Thus the fact that he cannot change the world he perceives becomes evidence for some higher power that causes and maintains the world.

Berkeley divided human knowledge into two categories: ideas and spirits. Ideas are things that can be perceived whereas spirits cannot. Our souls perceive ideas but they themselves can only be comprehended by inner feelings or reflection.

John Locke used the term 'idea' to mean the object of reflection. (e.g. 'I have an idea for a novel')
Berkeley restricted the meaning of 'idea' to the passive objects of perception and used the term 'notion' when talking about spiritual substance and its operations. For Berkeley, we have no idea of spirits (we do not directly perceive them) but we do have a 'notion' of them.

Berkeley admitted that idealism could lead to doubts about the existence of other minds:

It is granted we have neither an immediate evidence nor a demonstrative knowledge of the existence of other finite spirits. (Three Dialogues Between Hylas and Philonous)

But he thought it was possible to use arguments based on analogy to justify a belief in other people having similar inner lives to the one to which we have immediate and privileged access.