As found in his book, the three Dialogues between Hylas and Philonous against the skeptics and atheists
In this book, the question addressed by Berkeley is about reality, that is, about what is. He starts by telling us a skeptic is one who doubts of everything.
In the first dialogue, the two want to settle the question of whether a thing can be said to exist without being perceived. Here is a dialogue between the two
Hylas: To exist in one thing and to be perceived another
Phil: I speak with regard to sensible things only. And of these I ask, whether by their real existence you mean a subsistence exterior to the mind and distinct from their being perceived?
Hylas: I mean real absolute being, distinct from, and without any relation, to their being perceived.
Phil: Heat therefore, if it be allowed a real being, must exist without the mind?
Hyl: It must
The dialogue continues to cover taste, odours, sound and colours, matter, extension, solidity and so on.
At the conclusion of the first dialogue, Hylas admits that he no idea can exist without the mind to which Phil tells him that by his arguments he denies the reality of sensible things since he made it consist in an absolute existence exterior to the mind.
Following Hylas’ above concession, Phil in the second dialogue suggests to him that
[..]to me it is evident for the reasons you allow of, that sensible things cannot exist otherwise than in a mind or spirit. Whence, I conclude, not that they have no real existence, but that, seeing they depend not on my thought, and have all existence distinct from being perceived by me, there must be some other mind wherein they exist. As sure, therefore, as the sensible world really exists, so sure there is an infinite omnipresent spirit who contains and supports it.
I don’t agree here with Berkeley, the world is my idea and the argument for the existence of an omnipresent spirit that contains and supports the world is unwarranted.
After the above comment by Phil, Hylas says
What! This is no more than I and all Christians hold, nay, and all others too who believe there is a god and that he knows and comprehends all things.
Phil disagrees with him, he argues
Men commonly believe that all things are known or perceived by god, because they believe the being of a god; whereas I, on the other side, immediately and necessarily conclude the being of a god, because all sensible things must be perceived by him.
In saying this, Phil declares a triumph against atheism and goes ahead and says
But that–setting aside all help of astronomy and natural philosophy, all contemplation of the contrivance, order, and adjustment of things–an infinite Mind should be necessarily inferred from the bare EXISTENCE OF THE SENSIBLE WORLD, is an advantage to them only who have made this easy reflexion: that the sensible world is that which we perceive by our several senses; and that nothing is perceived by the senses beside ideas; and that no idea or archetype of an idea can exist otherwise than in a mind. You may now, without any laborious search into the sciences, without any subtlety of reason, or tedious length of discourse, oppose and baffle the most strenuous advocate for Atheism. Those miserable refuges, whether in an eternal succession of unthinking causes and effects, or in a fortuitous concourse of atoms; those wild imaginations of Vanini, Hobbes, and Spinoza: in a word, the whole system of Atheism, is it not entirely overthrown, by this single reflexion on the repugnancy included in supposing the whole, or any part, even the most rude and shapeless, of the visible world, to exist without a mind? Let any one of those abettors of impiety but look into his own thoughts, and there try if he can conceive how so much as a rock, a desert, a chaos, or confused jumble of atoms; how anything at all, either sensible or imaginable, can exist independent of a Mind, and he need go no farther to be convinced of his folly. Can anything be fairer than to put a dispute on such an issue, and leave it to a man himself to see if he can conceive, even in thought, what he holds to be true in fact, and from a notional to allow it a real existence?
Their dialogue continues to tackle MATTER. Here Hylas is forced to concede yet again that what is commonly known as matter doesn’t exist. Phil says in part
HYL. Hold, let me think a little–I profess, Philonous, I do not find that I can. At first glance, methought I had some dilute and airy notion of Pure Entity in abstract; but, upon closer attention, it hath quite vanished out of sight. The more I think on it, the more am I confirmed in my prudent resolution of giving none but negative answers, and not pretending to the least degree of any positive knowledge or conception of Matter, its WHERE, its HOW, its ENTITY, or anything belonging to it.
PHIL. When, therefore, you speak of the existence of Matter, you have not any notion in your mind?
HYL. None at all.
PHIL. Pray tell me if the case stands not thus–At first, from a belief of material substance, you would have it that the immediate objects existed without the mind; then that they are archetypes; then causes; next instruments; then occasions: lastly SOMETHING IN GENERAL, which being interpreted proves NOTHING. So Matter comes to nothing. What think you, Hylas, is not this a fair summary of your whole proceeding?
HYL. Be that as it will, yet I still insist upon it, that our not being able to conceive a thing is no argument against its existence.
As this second dialogue ends, Hylas says in submission
I acknowledge you have proved that Matter is impossible; nor do I see what more can be said in defence of it. But, at the same time that I give up this, I suspect all my other notions. For surely none could be more seemingly evident than this once was: and yet it now seems as false and absurd as ever it did true before. But I think we have discussed the point sufficiently for the present. The remaining part of the day I would willingly spend in running over in my thoughts the several heads of this morning’s conversation, and tomorrow shall be glad to meet you here again about the same time.
The third dialogue is continuation on matter and god and at the end we hear
PHIL. I do not pretend to be a setter-up of new notions. My endeavours tend only to unite, and place in a clearer light, that truth which was before shared between the vulgar and the philosophers:–the former being of opinion, that THOSE THINGS THEY IMMEDIATELY PERCEIVE ARE THE REAL THINGS; and the latter, that THE THINGS IMMEDIATELY PERCEIVED ARE IDEAS, WHICH EXIST ONLY IN THE MIND. Which two notions put together, do, in effect, constitute the substance of what I advance.
HYL. I have been a long time distrusting my senses: methought I saw things by a dim light and through false glasses. Now the glasses are removed and a new light breaks in upon my under standing. I am clearly convinced that I see things in their native forms, and am no longer in pain about their UNKNOWN NATURES OR ABSOLUTE EXISTENCE. This is the state I find myself in at present; though, indeed, the course that brought me to it I do not yet thoroughly comprehend. You set out upon the same principles that Academics, Cartesians, and the like sects usually do; and for a long time it looked as if you were advancing their philosophical Scepticism: but, in the end, your conclusions are directly opposite to theirs.
PHIL. You see, Hylas, the water of yonder fountain, how it is forced upwards, in a round column, to a certain height; at which it breaks, and falls back into the basin from whence it rose: its ascent, as well as descent, proceeding from the same uniform law or principle of GRAVITATION. just so, the same Principles which, at first view, lead to Scepticism, pursued to a certain point, bring men back to Common Sense.
The three dialogues are arguments against materialism and are an attempt to establish the existence of god as was shown above where Phil argues there must be a universal mind that perceives all things. I don’t see why this is necessary. There is no justification as I said before for coming to the conclusion of there being a mind that conceives everything in the universe.
I recommend that if you have time this year, you should make it one of your to read books, regardless of your beliefs or non beliefs.