‘Beauty is truth, truth beauty’ is perhaps the most famous statement John Keats ever wrote. But what do these words mean? They form part of the concluding couplet to his poem ‘Ode on a Grecian Urn’, perhaps the most famous of his five Odes which he composed in 1819, which was something of an annus mirabilis for Keats’s creativity:
‘Beauty is truth, truth beauty,—that is all
Ye know on earth, and all ye need to know.’
‘Ode on a Grecian Urn’ is about how great art transcends our own short, mortal lives. When Keats and his generation are all long dead, this Grecian urn will remain for future generations who experience similar woes to Keats, and the urn will be ‘a friend to man’, a consolation. After all, it has endured since the heyday of ancient Greece, over two millennia ago, until the time of Keats himself, in the early nineteenth century.
In the last two lines of ‘Ode on a Grecian Urn’, the urn ‘speaks’, as Keats sums up the message of this timeless work of art as:
‘Beauty is truth, truth beauty,—that is all
Ye know on earth, and all ye need to know.’
In other words, beauty is all we need in order to discover truth, and truth is itself beautiful. This is all we, are mere mortals, know, but it’s all we need to know: we shouldn’t impatiently go in pursuit of answers which we don’t need to have. Implied in these last lines of Keats’s poem is the suggestion that we shouldn’t attempt to find concrete answers to everything; sometimes the mystery is enough.
Indeed, the words ‘on earth’ imply that there is perhaps more to be discovered beyond the earthly and temporal confines of mortal life: that there is another plane, the heavenly or ethereal one, where other truths and other knowledge will be 
discovered. The Grecian urn, though shaped by mortal human hands, seems to be a hotline to some divine plateau, even though it refuses to vouchsafe the secrets it ‘knows’. There’s the air of a father patting his child on the head and saying, ‘There, there, don’t you worry your little head about any more than this fact: that beauty is truth, and truth is beauty.’
However, should we take Keats’s – or the urn’s – words at face value? Some critics of the poem have suggested that these last two lines are ironic: they are, after all, spoken not by Keats himself (or by his speaker) but by the urn, to which Keats has attributed them. In such an interpretation of the poem, Keats is dissatisfied with the ‘Cold Pastoral’ of the urn which smilingly sits there, with its pretty pictures, and says, ‘Beauty is truth, truth is beauty, and that’s all you’re getting. Like it or lump it.’ (We’re paraphrasing, of course.)
If we follow such an analysis, the logical conclusion is that Keats is pouring scorn on the urn for being so tight-lipped, so smugly and wilfully ‘silent’, in its refusal to tell more about the history and culture (and perhaps more) that it depicts. Is Keats, then, bemoaning the limits of art, lamenting the fact that it offers only partial ‘messages’ and doesn’t provide us with wholesale meaning?
This reading seems unlikely, as we can see if we turn to Keats’s beliefs about art, expressed elsewhere in his letters. ‘Ode on a Grecian Urn’ is a fine poetic example of Keats’s theory of ‘Negative Capability’, a concept he outlined, and defined, in a letter of December 1817:
several things dovetailed in my mind, & at once it struck me, what quality went to form a Man of Achievement especially in Literature & which Shakespeare possessed so enormously – I mean Negative Capability, that is when a man is capable of being in uncertainties, Mysteries, doubts, without any irritable reaching after fact & reason – Coleridge, for instance, would let go by a fine isolated verisimilitude caught from the Penetralium of mystery, from being incapable of remaining content with half knowledge.
Keats’s Negative Capability is evident in ‘Ode on a Grecian Urn’ in the ‘mysterious’ nature of the urn, which offers the viewer partial glimpses and hints of a long-vanished civilisation. It isn’t necessary to learn more than the fact that beauty is truth, and truth in turn is beautiful: this is, after all, enough.
Indeed, he reminds us that imagined melodies are sweeter than those which we physically hear, which rarely live up to our expectations. There’s something to be said for dwelling in innocence, or even partial ignorance. Keats liked the fact that not all facts are readily available to us. Elsewhere, in his long narrative poem ‘Lamia’, he criticised science for removing the mystery of the rainbow (he’s thinking specifically of Isaac Newton’s work unravelling the structure of the colour spectrum):
Philosophy will clip an Angel’s wings,
Conquer all mysteries by rule and line,
Empty the haunted air, and gnomèd mine –
Unweave a rainbow, as it erewhile made
The tender-person’d Lamia melt into a shade …
So if those final two lines of ‘Ode on a Grecian Urn’ are ironic, it’s because they are too glib a summary of the urn’s worth and meaning; not because Keats dislikes art’s reluctance to offer up wholesale meanings, facts, or philosophical solutions. Beauty is truth, and the truth that the urn reveals to him is beautiful. That is all he, or any of us, needs to know.