Sometimes we find a poet, or a painter, or a musician who functions like a key that unlocks a part of ourselves we never knew was there. The experience is not like learning to appreciate something that we once found difficult or rebarbative, as we might conscientiously try to appreciate the worth of The Faerie Queene and decide that yes, on balance, it is full of interesting and admirable things. It’s a more visceral, physical sensation than that, and it comes most powerfully when we’re young. Something awakes that was asleep, doors open that were closed, lights come on in all the windows of a palace inside us, the existence of which we never suspected.

So it was with me in the early 1960s, at the age of 16, with William Blake. I came to Blake through Allen Ginsberg, whose Howl I read half aghast, half intoxicated. I knew who Blake was; I even had an early poem of his by heart (“How Sweet I Roam’d from Field to Field”); I must have come across “The Tyger” in some school anthology. But if Blake could inspire the sort of hellish rapture celebrated and howled about by Ginsberg, then he was the sort of poet I needed to read. Hellish rapture was exactly what I most wanted.

Accordingly, I searched for Blake in the nearest bookshop, which was WH Smith in Barmouth, in what used to be called Merionethshire. There was no Blake there. The local library didn’t help, either. It wasn’t until I went to London on a rare holiday visit that I found a Selected Blake in a small American paperback, edited by Ruthven Todd and published by Dell in their Laurel poetry series. If I’d bought it in the USA it would have cost 35c; I can’t remember what I paid for it in Foyles, but it must have been well under a pound. It’s on the table next to me now, battered, the cover coming apart, the cheap paper flimsy and yellowing. It’s the most precious book I have. A couple of years later I acquired, as a school prize, Geoffrey Keynes’s Nonesuch Press Complete Prose and Poetry of William Blake, a handsome hardback now almost as battered, almost as yellowed, almost as precious. But I could put the Dell Blake in my pocket, and for years I did.

Urizen measuring out the material world (c1794) from The Ancient of Days by William Blake. Photograph: The Gallery Collection/Corbis

Thanks to those books, and thanks to my encounter with Ginsberg, and thanks further back to the enlightened local education authority that sent a library van around to the secondary schools in Merionethshire so that I could choose from their shelves the anthology (Donald Allen’s The New American Poetry 1945-1960: still in print, still irreplaceable) that contained Howl – thanks to those things, I discovered what I believed in. My mind and my body reacted to certain lines from the Songs of Innocence and of Experience, from The Marriage of Heaven and Hell, from “Auguries of Innocence”, from Europe, from America with the joyful immediacy of a flame leaping to meet a gas jet. What these things meant I didn’t quite know then, and I’m not sure I fully know now. There was no sober period of reflection, consideration, comparison, analysis: I didn’t have to work anything out. I knew they were true in the way I knew that I was alive. I had stumbled into a country in which I was not a stranger, whose language I spoke by instinct, whose habits and customs fitted me like my own skin.

That was 50 years ago. My opinions about many things have come and gone, changed and changed about, since then; I have believed in God, and then disbelieved; I have thought that certain writers and poets were incomparably great, and gradually found them less and less interesting, and finally commonplace; and the reverse has happened, too – I have found wonderful things, unexpected depths of treasure, in books and poems I had no patience to read properly before.

But those first impulses of certainty have never forsaken me, though I may have been untrue to them from time to time. Indeed, they have been joined by others, and I expect to go on reading Blake, and learning more, for as long as I live.

One such impulse of certainty concerns the nature of the world. Is it twofold, consisting of matter and spirit, or is it all one thing? Is dualism wrong, and if so, how do we account for consciousness? In the opening passage to Europe: A Prophecy, Blake recounts how he says to a fairy “Tell me, what is the material world, and is it dead?” In response the fairy promises to “shew you all alive / The world, where every particle of dust breathes forth its joy.” This is close to the philosophical position known as panpsychism, or the belief that everything is conscious, which has been argued back and forth for thousands of years. Unless we deny that consciousness exists at all, it seems that we have to believe either in a thing called “spirit” that does the consciousness, or that consciousness somehow emerges when matter reaches the sort of complexity we find in the human brain. Another possibility, which is what Blake’s fairy is describing here, is that matter is conscious itself.

But why shouldn’t it be? Why shouldn’t consciousness be a normal property of matter, like mass? Let every particle of dust breathe forth its joy. I don’t argue this, I perceive it.

Things that are living, whose bodies however small pulse with that same energy, are capable of even more joy than the particle of dust:

How do you know but ev’ry Birdthat cuts the airy way,

Is an immense world of delight,clos’d by your senses five?

(The Marriage of Heaven and Hell)

That perception carries a moral charge, which is most clearly expressed in “Auguries of Innocence”, a poem not published during Blake’s lifetime. I take it to be one of the greatest political poems in the language, for the way it insists on the right to life and freedom without qualification, uniting large things and small, and shows the moral connections between them:

A Robin Red breast in a Cage

Puts all Heaven in a Rage.

A dog starv’d at his Master’s Gate

Predicts the ruin of the State.

Each outcry of the hunted Hare

A fibre from the Brain does tear.

The wanton Boy that kills the Fly

Shall feel the Spider’s enmity.

Each couplet is a hammer-blow in the cause of a justice that includes all creatures, and tells the truth about power: “Nought can deform the Human Race / Like to the Armour’s iron brace.”

And who can forget the last Labour government’s infatuation with gambling and super-casinos, embodied in a photograph of a secretary of state beaming broadly beside a roulette wheel? “The Whore & Gambler, by the State / Licenc’d, build that Nation’s Fate.”

Again, this is not a matter of arguing so much as of perceiving. It’s a matter of vision.

And when it comes to vision, we need to be able to see contrary things and believe them both true: “Without Contraries is no progression” (The Marriage of Heaven and Hell), despite the scorn of rationalists whose single vision rejects anything that is not logically coherent. Blake was hard on single vision:

Now I a fourfold vision see

And a fourfold vision is given to me;

Tis fourfold in my supreme delight

And threefold in soft Beulahs night

And twofold Always. May God uskeep

From Single vision and Newtonssleep!

(“Letter to Thomas Butts”)

Fourfold vision is a state of ecstatic or mystical bliss. Threefold vision arises naturally from Beulah, which, in Blake’s mythology, is the place of poetic inspiration and dreams, “where Contrarieties are equally True” (Blake, Milton). Twofold vision is seeing not only with the eye, but through it, seeing contexts, associations, emotional meanings, connections. Single vision is the literal, rational, dissociated, uninflected view of the world characteristic, apparently, of the left hemisphere of the brain when the contextualising, empathetic, imaginative, emotionally involved right brain is disengaged or ignored. (I owe this observation to Roderick Tweedy’s remarkable The God of the Left Hemisphere (2012), and through that to Iain McGilchrist’s The Master and His Emissary (2009), a profound examination of the differences between the left hemisphere of the brain and the right.)

Image credit: William Blake Christ in the Sepulchre, Guarded by Angels (1805). Courtesy of V&A Images

I believe this, too. Single vision is deadly. Those who exalt reason over every other faculty, who condemn those who don’t respond to life with logic but allow themselves to be swayed by emotion, or who maintain that other ways of seeing (the imaginative, the poetic, etc) are fine in their place but the scientific is the only true one, find this position ridiculous. But no symphony, no painting, no poem, no art at all was ever reasoned into existence, and I knew from my youth that art of some kind was going to be the preoccupation of my life. Single vision would not do. “I will not Reason & Compare: my business is to Create” (Blake, “Jerusalem”).

If I didn’t know that from experience when I was young, I know it now. We find the truth of it most forcibly when twofold or threefold vision fails, and we fall into the state described by that great Blakeian WB Yeats as “the will trying to do the work of the imagination”. It’s a condition, I dare say, in which most writers and artists have found themselves marooned from time to time. To get lost in that bleak state when inspiration fails is to find yourself only a step away from an even darker labyrinth, which goes by the entirely inadequate name of depression. A savage deadly heaviness, a desolation of the spirits, an evil gnawing at the very roots of our life: if we’re unlucky enough to feel that, we will know from experience that the opposite of that abominable condition is not happiness, but energy. “Energy is the only life, and is from the Body; and Reason is the bound or outward circumference of Energy. Energy is Eternal Delight.” (The Marriage of Heaven and Hell). In its absence, goodness, intellect, beauty – and reason, too – are listless, useless phantoms pining for the blood of life. When I had the misfortune to fall under the oppression of melancholia (another inadequate word), one of the things to which I owed my escape was an edition of the letters of Bernard Shaw, where I found energy abounding. I have loved him ever since.

With twofold vision it’s possible to see how contrary things could be believed. With threefold vision, with the inspiration that comes from the unconscious, from Beulah, it’s possible to believe them. I have found over many years that my way of writing a story, from what used to be called the position of the omniscient narrator, allows me a freedom that writing in the first person doesn’t permit. It means the telling voice can inhabit a multitude of different imaginative states. The voice that tells my stories is not that of a person like myself, but that of a being who is credulous and sceptical simultaneously, is both male and female, sentimental and cynical, old and young, hopeful and fearful. It knows what has happened and what will happen, and it remains in pure ignorance of both. With all the passion in its heart it believes contrary things: it is equally overawed by science and by magic. To this being, logic and reason are pretty toys to play with, and invaluable tools to improve the construction of the castles and grottoes it creates in the air. It scoffs at ghosts, and fears them dreadfully, and loves to call them up at midnight, and then laughs at them. It knows that everything it does is folly, and loves it all the same.

And thanks to the genius of William Blake, it knows that “All deities reside in the human breast”, and that “Eternity is in love with the productions of time” (The Marriage of Heaven and Hell). And it thinks that those things are worth knowing.

• William Blake: Apprentice & Master, takes place at the Ashmolean, Oxford from 4 December to 1 March 2015.