We know what life is: rough and smooth, ugly and beautiful, cheap and expensive. Likewise the world: land and sea, fantasy and reality, now and then. But modernity can blur those boundaries: just to take death - in the hospital, not on the gallows; few starve on the streets; most lynchings take place by social media. Wind back 600 years and the delineations were sharper: saint and sinner, master and servant, freedom and slavery. Kate Lyddon is something of a medievalist, and such distinctions course through her work. Indeed, her recent show at the Zabuldowicz

Collection revolved around wood spirits and bark witches. Lyddon, then, trades in the clash and reconciliation of oppositions. That, in philosophical terms, might make her a contrastivist of sorts. Contrastivism is an epistemological theory, which is to say it deals with how we gain our knowledge of the world. That theory’s adherents say that knowledge is not a relation of the obvious two places – not, for example, ‘she knows it is purple’ – but of three, eg ‘she knows it is purple rather than blue’. That implies that she might not know that ‘it is purple rather than magenta’ – those are different degrees of knowledge. So, in Lyddon’s case, we might say not simply ‘she knows it is beautiful’ but ‘she knows it is beautiful rather than ugly’. The contrasts are entwined. We might be reminded of the defence of God for allowing suffering: what is pleasure without the possibility of pain? Lyddon’s twist, though, is that beauty doesn’t merely operate in the context of ugliness, but that they are potentially interchangeable categories. Not only do we define the beautiful partly by reference to the ugly, but the ugly may come to be seen as beautiful.

Lyddon enacts this contrastivism through both content and materials. Her portraits, if that’s the right term for imagined faces, use the traditionally significant medium of oil on canvas - expensive enough in pre-modern times that having one’s likeness made was indicative of wealth and status. Just so, Portrait [Woebegone] is wearing a ruff and Portrait [Blood-Red] a crown. That sets up the expectation of flattery, seriousness and impressive form and colour. What we get, though, is a cast of curiously-hued oddballs who seem decidedly unlikely to have been able to pay for their depictions, or – we might assume – to want to be depicted. Their features are, on the face of it, ugly by conventional standards. Are they diseased? Lyddon takes an interest in freak shows, medical history and in disfiguring conditions such as epidermodysplasia verruciformis or Tree-man Illness. Or perhaps they’re wounded - we might think of the disturbing aesthetics of Henry Tonks’ paintings of World War I casualties.

And yet... isn't there also a certain allure here? Portrait [Peely-Wally]’s skin is a potentially cool blue, and the decoration which doesn't so much emphasise as take over the eyes could be a fashion of the future. The nose on Portrait [Liverish] is decidedly porcine, but perhaps our aesthetics should extend beyond the human, as well as beyond the narrow expectations of gender which these androgynous characters seem to evade. These figures are beautifully ugly. Or, looking in the other direction, consider how ugly beauty can seem: the inflated collagen lips, frozen Botox expressions and lurid orange tans arrived at in the name of beauty can push beyond its conventions into quite different territory.

And there’s another ambiguity: are these accurate portraits, or is this just how the artist has chosen to represent her subjects, reflecting a diversion into the pleasures of using her materials? Is it that the king's face is distorted to melting point in an eerie match for his elongated earrings, or has Lyddon exaggerated the earrings and carried that over into a face which replaces reality with a different potential for beauty - the painterly?

Lyddon’s sculpture, too, contains contrasts of both material and content. On the material side, ceramic and copper play off polystyrene and cast-off table legs. All the signs are that they are valued equally, and that Lyddon enjoys the way different materials provoke different responses. Clay-rather-than-polystyrene and polystyrene-rather-than-clay work more strongly for Lyddon in the context of how they could have been each other. So far as content goes, where the portraits do, by and large, appear whole, the sculptural characters are incomplete. Yet maybe we're in the superficialising grip of conventional expectation once more. The ‘aesthetic of the fragment’ is well known, but isn’t conventionally applied to the living or the new.

Why not go further, by collaging together those chosen elements and – embracing the grotesque – arrange body parts as surreal conjunctions of found objects? Those two aspects are plain in Lower Limb with Spoon and Straw, in which a onelegged form, resplendent as a limb can be in scarlet Lycra leggings, relies on a copper pipe as an implausibly thin stand-in for his second leg. He’s lost his torso and arms entirely, and his head to the extent that it’s rolling on the floor. Where it used to be attached, the neck’s severance reveals the crudeness of the polystyrene of which he’s made.

Put the paintings and sculptures together, and you won’t be surprised to learn that Lyddon used to make paintings with all sorts of collage elements applied to generate that clash and reconciliation of opposites: it felt like Bacon meets Klee meets Quasimodo meets My Little Pony all on the canvas with scrawled lyrics to boot. Now paintings and objects have gone their separate ways, but come together as an installation in which copper tubes and cutlery act as connectors. The pipes remind us of plumbing inside the body, and their striping of a barber's pole. It’s said that such signs originally mimicked the bandaging after the medieval service of bloodletting (barber, surgeon and dentist being less distinct roles 600 years ago). If the copper tubes, then, stand in for the body’s processes of flow and waste, then the spoons stand in for sustenance. A circuit is proposed, related to the biggest contrast of all.

There’s a play on the nobility of being ‘born with a silver spoon in the mouth’, while making it plain that - however valuable the implement - it all goes down the same way. As do we, in Larkin’s words, ‘down the long slide / To happiness, endlessly’ – in High Windows’ elision of another contrast, from the life giving force of sexual discovery towards the only conclusion of our pursuits.

Cheer up, though! For Lyddon, like Larkin, brings an irrepressibly enjoyable relish to her account of the human condition. There’s more comedy than tragedy in her contrastivist account of how history has brought us to this beautifully ugly pass. If all human experience, bodily and psychic, feeds through Lyddon and into her art, then On Drool is ‘about life’. It sounds trite to say so, but that’s how the work takes on its own – far from trite – life in practice. And, after all, what other subject is there?