I was first introduced to the work of David Shrigley by his then publisher, Julian Rothenstein at Redstone Books. Julian sent me the proofs of what was to become Why We Got the Sack from the Museum and asked me if I'd consider writing an introduction for the finished book. I was immediately ensorcelled by the singularity of the Shrigley worldview: here were pictures that had a bewilderingly complex naivete about them – it was as if a preternaturally intelligent child were rendering the attempts of a smart-aleck adult to draw like a kid. The thick black felt-tip line divagated across the pictorial space yet always arrived at precisely the right place, nailing to a fixed point one or other of life's great issues: sex and death, right or wrong. There seemed something altogether just about the Shrigley style, which united dodgy orthography – misspellings simply being scratched out and wonkily rewritten – with a sense of authority; for, no matter what the confusions and moral turpitudes of his toothy men and malformed women, his scrawled beasts and banjaxed bestiary, behind it all, one felt certain, lay a shrewd maker.

I loved – and continue to love to this day – the way in which Shrigley's work crumples into a tight ball and tosses across the studio (in the general direction of the wastepaper basket) all of the squeaky confusions that squiggle about contemporary so-called "fine art". At one level his works – and this includes the sculptures, installations and photography – are nothing more or less than cartoons. After all, they unite words and pictures together to produce effects that are usually – but by no means always – humorous. But, judged by the standards of most cartoonists, Shrigley doesn't really make the grade: a cartoon should have an effortless if expressive line betokening the art that annuls any artistry. By contrast, Shrigley's line is smudged and scumbled. Then again, the works of many of his conceptual contemporaries – one thinks of Hirst, Lucas, the Chapmans et al – are just as cartoonish, yet in the pomposity of their high style, and in the industrialisation of their heavily assisted production, they possess none of the physicality and immediacy of Shrigley's. When you look at a Shrigley work, you are right away assured of his input – each one bears the impress of his hand and its guiding inspiration.

Over the years, I've continued to follow Shrigley's career, and while I've met him a couple of times, I've never spoken to him for long. I'm the proud possessor of a couple of Shrigley originals; and believe me, it's worth seeing the drawings in the flesh, although I accept that, perhaps more than most artworks, they work nearly as well in reproduction. So, it was with great pleasure that I invited him to my south London home for an extended conversation in advance of the announcement of this year's Turner prize, for which he has been shortlisted. Actually, pleasure is an understatement – long before he arrived, my 12-year-old son (a Shrigley fan as well) and I were cackling with delight at the thought of the Very Funny Joke we had planned for him.

I'm Dead (2010), by David Shrigley. Photograph: Olivia Harris/Reuters

At the centre of Brain Activity, last year's Shrigley show at the Hayward Gallery, stood a small, apparently stuffed Jack Russell dog holding a sign that proclaimed "I'm Dead". To welcome Shrigley to our house, we had attached a sign to our very yappy and aggressive Jack Russell that read simply "I'm Alive", and when we opened the door to the artist, we unleashed the hound of humour. Shrigley managed a wry smile as the dog nipped at his ankles.

WS: Are your parents still alive?

DS: Yes, my mum and dad are alive and still together. They're both 73 and live in Oadby, a suburb of Leicester where I grew up, and they're retired.

WS: What did they do when they worked?

DS: My father was unable to explain to me in layman's terms what he did for a living. All I know is he did quality management, but fortunately he doesn't do that any more, so the burden of trying to explain it to me and other dullards is over.

WS: They say that all male novelists' first books are acts of parricide; do you think there's any element of that in your work?

DS: I don't know, there were certainly a lot of moral-conundrum-type things [in my work] to begin with – the Devil and God would appear – and my father is a fundamentalist Christian, so that inevitably had an effect on me.

WS: And your mother, too?

DS: My mother less so. She is an Anglican, but my dad goes to the evangelical church, where they speak in tongues and lay on hands.

WS: Did you experience a loss of faith, or have none to begin with?

DS: I had some faith when I was a young teenager, but by the time I got to 16 and started reading writers such as Camus, I could no longer call myself a Christian.

WS: But your father didn't shove it down your throat?

DS: Not really, no.

WS: He sounds all right.

DS: Yeah, he is quite good: when Jehovah's Witnesses would come round he'd say, "Come in, come in …", and pretty soon they'd leave of their own accord.

WS: Do you see much of your parents now?

DS: Not as much as we used to. We talk a lot on the phone, but we don't have any kids, whereas my sister does have kids, and we have a dog, so …

WS: How are they with dogs?

DS: Yeah, not so keen on dogs. They understand that we love the dog, but lots of things about the dog go unsaid.

WS: What things?

DS: The fact that the dog, called Inka, sleeps in the bed with us now.

WS: It's interesting that you don't have kids, given that your work often plays with notions of naivety and childlike perspectives.

DS: Yeah, and it has a following among 10-year-old boys; they get it, which I'm happy about. I guess in another life I would have had kids. I don't have anything against them, but stuff happens and you end up not having any.

WS: When you're working, do you think you're in some way channelling an inner child?

DS: Yeah, when people say, "Have you always worked like this?", I recall being four or five years old and sitting down and making a drawing. In a way, that activity remains the same, even though I'm a middle-aged guy now: a drawing is its own reward; it's not a means to an end. Drawing was fun when I was at infant school, and it's fun now.

WS: When you left Glasgow School of Art you were fed up with them for giving you a second-class degree – and you were working in the recognisably Shrigleyesque style at that point. Did you think: I'm going to take on the art world, end up winning the Turner prize and show 'em all?

DS: I think you realise quickly that art school is just a funny little bubble and the opinions of people who give you the marks are so subjective that to have an honours degree system for art is a bit ridiculous.

WS: You're refreshing among your peers in that you don't mind admitting you can't draw, but traditionally the capacity for draughtsmanship and formal composition would have been seen as a part of fine art education, wouldn't it?

DS: Yeah, but in my experience it's the illustration students who can draw, and the fine artists – some of whom have won the Turner prize – make me look like Rembrandt in their unwillingness to handle any materials.

WS: Indeed, you say you can't draw but your drawings bear strong evidence of the human touch. They're very physical.

DS: What I mean is that I'm not interested in objectively rendering three-dimensional space; I'm not very good at it, and I'm not a particularly good draughtsman, either. Obviously I make drawings that are graphically sophisticated, or at least say what they need to say, but it's a different activity from illustration.

WS: If I look at one of your drawings, I'm very conscious of the fact that it's not something that can be done by a machine. Did you consciously arrive at that style, given that the retreat from draughtsmanship is surely a retreat from what photography does and artists no longer need to?

DS: I suppose so. At art school, the stuff I was excited about was by Duchamp, Warhol and many others, but it was ideas-based art, and that's where you find my form of ideas-based art. When I left, I didn't have a studio, and it was just a practical thing: I thought: "Maybe I should just focus on these drawings, because I actually like doing these a lot more than trying to make the difficult sculptures and doing the large-format photography that I'd made at college." I felt I could say what I wanted to on a sheet of paper, sitting in my shared flat. And I thought: I'll make a book, so I just made the book on a Xerox machine and gave it out at the pub, and that's how it all started.

WS: Can you remember what you flogged it for in the pub?

DS: I think the seminal one was perhaps £3.50, which was quite a lot.

WS: How do you feel about being shortlisted for the Turner prize?

DS: I don't think it can be a bad thing. Lots of my friends have been nominated for it over the years, and I'm always very keen on it when they're in it, but sometimes they nominate nobody I've heard of, so does it matter that much? It takes up a lot of head space, given that it's a group exhibition and all you're exhibiting is a work that you've already made.

WS: Have you given them some of the stuff that was in your Southbank exhibition, Brain Activity?

DS: No, but I made a piece for a show at Cornerhouse in Manchester and that's gone into the Turner prize exhibition; it's a giant, badly proportioned life model that's two-and-a-half metres tall, blinks and pees into a bucket. People are invited to draw pictures of it and put them on the walls, so the installation is like an art school life‑class with loads of other people's work in it, and this weird kinetic, cartoon-like yet lifelike figure.

WS: What's that all about?

DS: It's about people getting involved [laughs].

WS: It's difficult not to see it as a wry comment on the nature of your own ineffable line.

Really Good, by David Shrigley. Photograph: James O Jenkins

DS: Well there are lots of levels to it. The life figure is very badly rendered and poorly proportioned, so it's my revenge: even if you're really good at life drawing – which obviously I wasn't – you can't do a lifelike drawing from it, as people won't know, unless they see it, that the original was so badly proportioned. Still, he's also quite handsome – he doesn't have any body hair – and he has a certain innocence.

WS: There's a lot of innocence in your world. Even the baddies are often amazed by their own moral turpitude as they do awful things.

DS: I've thought this all through life: there's only a cigarette paper between acceptable and unacceptable behaviour, and it's easy just to cross over and tumble down that hill the other side. Besides, if you've thought it, somebody's probably done it, which means that I'm unwittingly documenting reality. Then you listen to conversations in the pub and it's always like, "Aye but see, he didnae do anything but I had to hit him … ", and you're sat there thinking, "So, it was an unprovoked attack, but you're masquerading it as a preemptive strike in order to protect your safety and perhaps that of your friend." But it's that kind of unreasoning that interests me.

WS: What about exhibiting your work on the fourth plinth in Trafalgar Square: it strikes me as a bit risky because it's something of an artist's graveyard, isn't it?

DS: I can't help thinking it's really a great idea. The thing I've made is in some ways really stupid – well, obviously it's pretty stupid, because I made it. But I was asked to, and you get paid for the proposal, then you get paid to make a big maquette – I made a large bronze one – and they give you a scale model of the fourth plinth, and you make your thing to go on it, and it gets commissioned; it's in Trafalgar Square and everybody sees it, which is totally mental.

WS: Yeah, but haven't almost all of the works have been diminished by the context?

DS: I like the weird ambiguity of that context, but more importantly everybody sees it. It's in Trafalgar Square, which remains strangely context-free for a lot of people. It's just the centre of London, which makes it like showing in a gallery, in a funny sort of way.

WS: Describe the piece for me.

DS: It's a giant thumbs-up like this [he makes the gesture], truncated and badly rendered but still lifelike. Except the thumb is so long it mirrors Nelson's Column. The piece is also bronze with the same patina as all the other bronzes, and it's called Really Good. I'm hoping it'll be a self‑fulfilling prophecy about London, whereby if I say it's really good, then it'll become really, um, good.

• The Turner prize exhibition takes place from 23 October 2013 to 5 January 2014 at Ebrington, Derry‑Londonderry.