It’s a line of Anne Stevenson’s. I remember it but I can’t for the life of me find the poem.

And since I wrote that, I’ve remembered whose line it really is. Not Anne’s, despite the fact that she has a number of particularly good dream poems. Sometimes I think my entire life is a process of half-remembered lines.

But it’s fitting that I couldn’t remember the precise provenance of this one, because when I first read it, (in ‘Five Dreams’ in Robert Nye’s 1976 collection, Divisions on a Ground) I felt I’d heard it already. I thought perhaps it was a half-quotation, or maybe just doing what poetry often does, drawing on the deep well of common phrase and cadence, so what comes up feels hauntingly familiar.

But I wanted to find the line again because I was thinking about dream poems, for which I’ve always had a predilection. Indeed, I’ve written a number myself, though nowhere near as many dream poems as I’ve had dreams.

I’ve found it now but my finding was less decisive than I thought. It’s in Nye’s Divisions on a Ground, and then it’s also in the Hamish Hamilton Collected (1989) but substantially different that is to say the key line is the same but the five dreams are slightly, or even completely in some cases, different. And in the more recent version (not included in The Rain and the Glass, 2004), the poet doesn’t say in the final stanza, “I dreamt a dream. I know what it means” as he did in the earlier version. Instead Nye concludes:

I dreamt a dream, what can it mean?
I dreamt I was a dry white bone
Which Love used as her flute.

Creepy. Why do some dreams demand to turn themselves into poems, when others fade? It’s probably that feeling – I dreamt a dream, what can it mean? – the sense of huge import, the feeling the dream is telling you something you need to understand. Cover of Freud's book on dreams

That feeling was around long before 1899 when Freud tackled the business with such far-reaching consequences. Anne Stevenson prefaces Stone Milk, her 2007 collection, with a quotation from 14th century Piers Plowman, “Then came a dream to me, marvellously I dreamed / [ . . . ] A fair field full of folk I found there between”. Significant dreams in the Old Testament of the Bible are even older, of course, which is how Joseph got his dreamcoat and is still singing about it in the twenty-first century.

But what about that experience where you dream you are writing the poem, and (in your sleep) you commit it to memory intending to put it on paper in the morning? You may even half-wake and scribble a few lines on the note pad at the side of the bed. The cold light of day almost invariably reveals these lines to be tripe. (‘Eid Ma Clack Shaw’! Bill Callaghan has the last word on this.)

But sometimes a dream successfully crosses the divide – it gets out of sleep mode and into a poem, where it still pulls its weight in the waking world. There are several reasons why such a poem is potent, I think. One is that the poet isn’t consciously choosing the components, so less control is exercised. The poet isn’t interfering.

A second advantage is the absence of deliberate intent. The writer hasn’t got designs on the reader, or at least not in the ordinary way. The writer is merely trying to present the dream as a shared puzzle.

And there’s the delight of the surreal. Dreams, by their very nature, specialize in surreality, and this breaks the mould of ordinariness – poems are always trying to do that. So the dream scores points there too.

In the middle of the surreal, real symbols. Dreams – at least the kind you want to write down – haunt you with visual emblems (or so it seems). I have recurrent dreams about a house with cellars and attics, secret stairs and hidden passages, and, as John Lennon said, I’m not the only one. Poems favour symbols because they accumulate meanings like a rolling snowball. And multiplicity of meaning, as we all know, is poetry’s favourite stamping ground.

Then there’s the business of narrative. Memorable dreams have a sort of story line, and sometimes there’s even a resolution. I can think of some marvellous dream poems that take full advantage of that – and immediately Edwin Muir’s The Combat leaps to mind, a poem you understand instantly on more than one level.

So far I’ve carefully avoided mentioning visions. But we have an age-old tradition of those too and the difference between a dream and a vision is slight. When dream acquires vision status it is powerful indeed and even has God connotations. Scary.

In a more down to earth sense, there’s fairly wide-spread agreement – this may be rational or purely self-indulgent – that the writing of poetry involves an altered state of consciousness. That is to say, not the usual way of thinking or feeling. Various legal and illegal substances can assist in this, and some produce noteworthy creations. ‘Kubla Khan‘ (subtitled ‘A Vision in a Dream’) was, according to Coleridge, wholly realized in sleep and only written down when he woke up. It seems clear opium had something to do with the exotic strangeness. (I am not recommending this.)

Meditation can alter consciousness too, of course, though it tends to float you away from words rather than towards them. But dreams take the biscuit. If your consciousness isn’t altered when you’re asleep, I don’t know when it is. And sometimes something extraordinary emerges as a result. No need to worry about this. The dream will tell you in no uncertain terms if it requires to be written down. Unlike most dreams, you won’t be able to forget it and, once you’ve written it down, neither will I.