What is so special about Scottish theatre? That was a question I posed in 1995 in the introduction to Made in Scotland, an anthology of Scottish plays edited by me and Ian Brown, the then artistic director of the Traverse Theatre. We had selected four plays – The Cut by Mike Cullen, The Life of Stuff by Simon Donald, Bondagers by Sue Glover and Julie Allardyce by Duncan McLean – and having billed it as a specifically Scottish collection, I felt duty bound to explain what the term 'Scottish' actually meant. Then, as now, I was at a loss.

After all, what possible connection could you make between a political drama about life after the miners' strike, a comedy set in a drug-fuelled night club underworld, a pastoral evocation of 19th century farming practices and a play about the off-shore Aberdeen oil industry? There was no unifying factor.

But the question was important. In those pre-devolution days there were two political impulses. The first was to recognise Scotland as a distinct cultural unit, a society with a sense of otherness, one that could produce books with titles such as Made in Scotland. Those of us who lived in the country found that to be self-evident – we just instinctively felt that, of course, Scotland was different. Culturally, socially, politically, geographically . . . the population's focus was in a different place to the rest of the United Kingdom and, indeed, the world. That was easy. But the second impulse was to find the evidence to justify such a distinction. If Scotland was really so distinct, surely it would have a body of literature, of art, of music, of drama that would be equally distinct. Yet for me the evidence proved nothing.

The case may or may not be made for literature, art and music, but for drama it is simply not possible to identify theatrical genes unique to the Scottish stage. Is it so difficult to imagine Sue Glover growing up in Ireland, Simon Donald in London, Mike Cullen in Wales, Duncan McLean in Grimsby? Yes, there would be changes, but a few linguistic tweaks here, a few altered references there and their 'Scottishness' would quickly be ironed out. You cannot look collectively at those playwrights and say they have any equivalent, say, to the lyricism of the Irish, the moroseness of the Russians or the philosophic enquiry of the French. Those national tags are certainly reductive clichés, but Scottish playwrights of the 1980s and 1990s are just too diverse for any similar reductive cliché to stick.

That is partly because of the absence of a compelling Scottish repertoire. There is no icon of Scottish drama against which all new work must be measured. There is no Playboy of the Western World, no O'Casey trilogy, no Waiting for Godot. It is safe to say that JM Barrie's Peter Pan holds no greater sway in Scotland than it does anywhere else. It is not a requirement for budding Scottish playwrights to be acquainted with the work of James Bridie. In short, there is no proto-drama from which all others sprang; no playwright to whom all Scottish playwrights aspire or react.

This is neither good nor bad. It just means that the many interesting and varied playwrights at work in Scotland cannot be subject to any simple categorisation. But what I felt in 1995 is that this variety is in itself a distinctive characteristic of the past two decades in Scottish theatre. The theatre economy has been small enough to retain its intimacy, its relationship with the audience, its sense of self, and big enough to sustain everything from the brilliant children's theatre of Andy Cannon's Wee Stories to the extravagant event-theatre of Angus Farquhar's NVA, the eloquent plays of Liz Lochhead and the European obscurities of the Citizens' Theatre studios.

It would be meaningless to argue that plurality was a uniquely Scottish trait, but it is palpably true that the specific circumstances of this country in the late years of the 20th century, and early years of the 21st, have allowed the flourishing of a rich and fertile plurality of theatrical endeavour. Scotland might not do well-made plays as well as the Irish, it might not do devised drama as well as the Quebecois, it might not do children's theatre as well as the Scandinavians, and it might not do experimental theatre as well as the Dutch, but it does do all of these things – occasionally superlatively – in a way that those other countries do not. Scottish theatre is a great all-rounder.

Take the case of David Greig. If one playwright embodied the spirit of plurality it is surely him. Leaving aside, for a moment, his collaborative work with Suspect Culture, the plays written under his own name seem purposely to have explored the great dramatic landmarks of the 20th century. I only mean to exalt the scale of his achievement when I suggest that The Architect took its cue from Ibsen, The Cosmonaut's Last Message to the Woman he once Loved in the Former Soviet Union from Brecht, The Speculator from Barker and Outlying Islands from Rattigan. Greig has always been conscious of operating in a European tradition (his early plays such as Stalinland and Europe made that explicit) and it has only been to his benefit that there is no overbearing Scottish tradition to constrain him.

If you then consider the output of Suspect Culture, which creates productions where acting, lighting, writing, music and direction are of equal importance, you see that Greig is a one-man plurality industry. From mould-breaking theatre to children's plays, from four-square dramas to elliptical studies of the fleeting nature of time, Greig is pre-programmed to surprise audiences and extend his own theatrical vocabulary.

Pulling the focus wider again, we see that Greig and Suspect Culture are just one facet of the wider Scottish theatre scene. Not just the playwrights, some of whom I discussed above, but the companies themselves represent eclecticism more than uniformity. There's Boilerhouse with its club-friendly physical experiments; Grid Iron with site specific ventures into school playgrounds and haunted closes; the Arches Theatre Company with its rough and ready curiosities; NVA with its boundary-busting excursions up mountains and into industrial wastelands; and so on and so on.

Perhaps it would not be hard to compile a similar list for other theatre communities, but it strikes me that there are social and geographic reasons why plurality should be the norm in Scotland. It is a small place with the bulk of its five million-plus population concentrated in the area in and around Glasgow and Edinburgh. This encourages two things: first, an intimate and sympathetic relationship with the audience; second, a ready exchange of artistic ideas. In bars, foyers, trains and galleries, it's very easy for visual artists to meet musicians to meet actors to meet dancers to meet directors . . . Just add water and before you know it you have Tony Graham's TAG, with its explorations of choreography, poetry and theatre in the early 1990s, or Gerry Mulgrew's Communicado, with its blend of music, art and stage tradition. Those are just two prominent examples of a trend that could be seen all over the place.

Just think of the actors. You are as likely to see an Una McLean, an Andy Gray or a Tam Dean Burn in a Christmas pantomime as a modern Canadian tragedy, a broad Scottish comedy or an experimental studio piece. Cross-fertilisation is the norm in a theatre culture that is built on nothing if not plurality.