They are called 'Outsider' artists, but a new exhibition argues that they are still capable of engaging with the world, writes Aidan Dunne

Inner Worlds Outside at the Irish Museum of Modern Art brings together works by some of the best known names in 20th-century art history with works by "Outsider" artists - that is, individuals producing art outside the conventional art world and usually living outside accepted social conventions, at the edges or beyond. That is, psychiatric patients, prison inmates, social recluses, visionaries.

In the nature of things, and particularly in recent years, some outsider artists have become well-known names in their own right, attracting a great deal of interest from scholars, commentators and, inevitably, collectors, as their work is publicised and exhibited.

The reclusive Henry Darger, for example, who worked as a hospital caretaker in Chicago, secretly composed a vast text epic, augmented by thousands of drawings and watercolours (he is discussed and illustrated in the show's accompanying publication). Posthumously, he has become something of a cult figure. Nathalie Merchant even wrote a song about him. His strange fantasy world, inhabited by armies of young girls, is a consistent if singularly odd fictional realm, a kind of very alternative Lord of the Rings.

He seems to fit the bill when it comes to Roger Cardinal's characterisation of outsider artists as the obsessive chroniclers of internal worlds. But the show's curator, Jon Thompson, argues the point when it comes to internal worlds. Just as all minds are alike, he suggests, so they address the same external world. Incarceration is no barrier to an imaginative engagement with "the wider world".

The work of Darger, and even more, perhaps, one of the best known Outsider artists, Adolf Wolfli, are actually accounts of the world we all inhabit. He makes an outline case for Wolfli's achievement as being on a par with that of the illuminators of The Book of Kells or Piet Mondrian's abstract paintings.

The implication is that we learn as much about reality from a paranoid mythological system such as Wolfli's (his writings cast him as a saintly saviour figure) as we do from "other descriptions of reality that are apparently endowed by a higher degree of objectivity".

But that "apparently" situates Thompson at the top of a very slippy relativist slope. It's worth mentioning, as well, that Cardinal recognises the necessity for links between the self-engrossed private domains of many Outsider artists and the wider world. Otherwise, their work would be blank and incomprehensible to us, and generally it is not.

Concerted interest in Outsider art coincided with the advent of modernity. The Romantic conception of the artist as a tortured, irrational, even demented individualist; developments in psychiatry; Freud's theories about the unconscious; Modernism's fascination with and need of the Other, exemplified in the Expressionists' infatuation with "primitive", unschooled, unmediated creativity - all these contributed to an enhanced concern with what was going on in the heads of those outside the world of everyday convention.

Dr Hans Prinzhorn's landmark study Artistry of the Mentally Ill was published in 1922. Subsequently, the Nazis sought to discredit art they didn't like by associating it with Outsider art, as well as African and other non-European art, incidentally anticipating the efforts such as this to negotiate a common ground between Insider and Outsider.

One of the catalysts in the increasing visibility of Outsider art in recent times has been the Musgrave Kinley Outsider Art Collection, initiated by Victor Musgrave, who organised the high significant Outsiders show at London's Hayward Gallery in 1979, and overseen since his death in 1984 by his companion, Monika Kinley (assistant curator on this show). As it happens, the collection has been on loan to the gallery since 1998 and has proved an ideal resource for the staging of Inner Worlds Outside.

Given the extensive links between various strands of 20th-century artists and Outsider strategies and states of mind, the exhibition is in a way pushing on an open door in setting out to demonstrate that the links between Insider and Outsider are more problematic than we might readily assume.

But Jean Debuffet, for example, an influential collector and exponent of Outsider art, was ambivalent about its status, and tried to keep it corralled away from the conventional art world of which he was very much a part.

One question is whether conscious appropriation of methodologies or ways of thinking is admissible in defining the putative categories of Insider and Outsider. As Jasper Johns observed: "Once an idea is given, you're stuck with it." He meant that, as an artist making work, you can't pretend that you don't know something. It is going to inform what you do. Is such a knowingness at variance with the notion of the Outsider artist? Certainly there are examples in the show which do come across as knowing, as though the artists are consciously adopting an Outsider position.

Other cases are more complicated than that. Louis Soutter's drawing Piece of Pompeian Wall Hanging is intriguing. With its woven grid patterns it prefigures later minimalist artists. Soutter spent 20 years of his life in a psychiatric clinic. But prior to that he had studied engineering, architecture, music and painting, and had worked as a musician and as an art teacher. Navajo artist Joseph Elmer Yoakum made beautiful, extraordinarily well composed, largely invented landscape drawings, sometimes loosely inspired by postcard views. But he only began to draw when he was aged 77, after a lifetime spent travelling as a circus worker and stowaway.

To a certain extent, both Soutter and Yoakum exhibit one of the common features evident in Outsider art: a clear compulsion to fill up every bit of blank space with marks and patterns. Yet to dismiss what they do as a kind of doodling on that basis would be wrong. There is much more going on there. It is in such complexities, where an individual's life feeds in intriguing ways into the work they make, that Inner Worlds Outside is strongest in terms of its stated aims. But the most important thing about it is that you can go and look for yourself, see a Paul Klee hanging next to a Dusan Kusmic, and form your own considered judgment.

Inner Worlds Outside is at the Irish Museum of Modern Art until Oct 15. The accompanying, richly illustrated book is available at €29.95