Idealism denies the existence of mind-independent objects. For the idealist, “to be is to be perceived”; objects are nothing more than our experiences of them.

The attraction of idealism is its economy. We don’t have direct access to the external world, it is generally agreed; all we can access directly are our experiences. Why, then, postulate the existence of anything beyond our experiences? The idealist refuses to do so, holding that our experiences don’t represent objects, but rather constitute them, that there is nothing beyond them.

For the idealist, then, objects only exist insofar as they are perceived. If I shut my eyes, then unless there is someone else perceiving the objects that surround me, those objects will cease to exist, at least until I reopen my eyes and perceive them once more.

Setting aside its initial implausibility, the main difficulty with this view is that it cannot explain the consistency of our experiences of the world. Why, when I reopen my eyes, do I see the same objects that I saw before? What causes me to perceive those objects rather than any others? Why, if two observers look in a single cupboard, and then compare what they saw, will both observers’ reports tally?

Berkeley, the most famous idealist, had both an answer to this problem and a way of avoiding the absurd suggestion that everytime I blink my study passes out of and back into existence in a fraction of a second: this answer is God.

God, according to Berkeley, is constantly perceiving everything. Though I may blink, and so stop perceiving my study, God continues to perceive it whether my eyes are open or shut. My study, therefore, never passes out of existence, for it is always perceived by God.

What is more, God explains the consistency in our perceptions. Though there may be no mind-independent objects causing our experiences, and so ensuring that our various experiences are mutually consistent, there is nevertheless something outside us causing our experiences and ensuring that they are consistent: God. God thus plays a central role in Berkeley’s idealism.