Summary: A Treatise Concerning the Principles of Human Knowledge (page 5)

Perhaps, then, this is merely a problem of vocabulary? For it sounds very harsh to say we eat and drink Ideas, and are clothed with Ideas ¹. Should Berkeley not simply call them things?

He replies that he uses this term because "thing" designates something active and existing outside the mind, whereas "idea" refers to what exists only within the mind and is inactive. The word therefore corresponds more accurately to the nature of the objects we perceive.

Three objections remain:

1) If fire burns us, does this not prove that it exists outside our mind? Berkeley points out that we feel pain in our minds.

2) We see things outside us at a distance, so they cannot belong to our mind. Berkeley once again invokes the dream argument: in dreams, we also see things at a distance, even though this corresponds to no external reality.

He also draws on a theory set out in detail in An Essay Towards a New Theory of Vision: we do not immediately perceive distance; it is only suggested to our Thoughts, by certain visible Ideas and by a Connexion taught us by Experience, they come to signify and suggest them to us ², in the same way that words in a language signify ideas.

The ideas that express distance only admonish us what Ideas of Touch will be imprinted in our Minds at such and such distances of Time, and in consequence of such or such Actions ³.

3) Does this mean that things disappear and reappear at any moment, as soon as we close our eyes or when no one is left to perceive them? Berkeley points out that this is already the case for secondary qualities in the philosophy of Locke and his followers. In his own doctrine, however, the problem does not arise, since another intelligence—the Author of Nature—perceives things even when we do not; they therefore retain their being.

It may seem surprising to claim that it is not fire that heats, but an intelligence. Yet Berkeley reminds us that many truths defy common sense: we say that the sun rises, whereas it is in fact the Earth that rotates.

Fire and heat are indeed two related ideas, but their relationship is not one of cause and effect—rather of sign and thing signified: fire is merely a sign that warns us of pain. As Berkeley states:

it is the searching after, and endeavouring to understand those Signs instituted by the Author of Nature, that ought to be the Employment of the Natural Philosopher, and not the pretending to explain things by Corporeal Causes ⁴.

This theory allows us to dispense with the endless speculations of philosophy, such as: Whether corporeal Substance can think? Whether Matter be infinitely divisible? ⁵

Scepticism is also dispelled, for the insoluble question at the root of scepticism—how do I know whether my ideas conform to external things?—no longer makes sense. On the contrary, sensible qualities are perfectly known, there being nothing in them which is not perceived ⁶.

Finally, this theory also undermines atheism, which is built upon materialism—the doctrine that makes a self-existent, stupid, unthinking Substance the Root and Origin of all Beings ⁷.

The natural sciences, on the other hand, remain entirely legitimate, for they seek to identify the laws of nature—which are like the language of the Supreme Intellect, through which He speaks to us and guides our actions towards the convenience and happiness of our lives. To study the world is to read the Volume of Nature ⁸. As Berkeley writes, this is why we need only open our Eyes to see the sovereign Lord of all Things with a more full and clear View, than we do any one of our Fellow-Creatures ⁹.

Wherever we direct our gaze, we perceive God. Nothing, therefore, could be more obvious than His existence.

¹ §38
² §43
³ §44
⁴ §66
⁵ §85
⁶ §87
⁷ §93
⁸ §109
⁹ §148