Thanks Marshall, I think we've finally got the message...

'A prophet is not without honour", says the Bible, "save in his own country." This was manifestly not true in the case of Marshall McLuhan, the Canadian cultural critic, who was born 100 years ago last Thursday, and was famous not only in his own country, but also abroad. In fact, he's the only public intellectual I can think of who played himself in a Woody Allen movie.

Film buffs will recall the wonderful sequence in Annie Hall, where Woody and Diane Keaton are queuing for a movie when a guy behind them starts opining pompously about McLuhan's description of television as a "high intensity or hot medium". Allen expresses to camera a desire to have a large sock full of horse manure close to hand, whereupon the guy asserts his right to express his opinion on the grounds that he teaches a course at Columbia on "TV, media and culture", a fact that – he asserts – gives his views on McLuhan a great deal of validity.

"That's funny," replies Woody, "because I happen to have Mr McLuhan right here." He goes over to a flipchart and pulls out the great man himself from behind it. "I heard what you were saying," says McLuhan to the Columbia man. "You know nothing of my work... how you ever got to teach a course in anything is totally amazing." The scene closes with Woody saying to camera: "Boy, if life were only like this."

As it happens, there have been many times in the past few years when it would have been useful to have had McLuhan to hand because, in a strange way, his insights into media seem more relevant now than they were in the 1960s when he sprang into prominence. His big idea, encapsulated in the baffling aphorism: "The medium is the message", was that the important thing about media is not the information they carry but what they are doing to us in terms of shaping our behaviour, the way we think and possibly also the way our brains are structured. McLuhan believed that this had been demonstrated by media that had dominated human society up to the 1960s – starting with print and culminating with broadcast television – and added the twist that TV was restoring the "sensory balance" that had been disrupted by print.

I never really understood McLuhan's views about television, preferring the perspective of one of his disciples, Neil Postman, who argued that the essential thing about the medium was that it had an infantilising effect, a view neatly encapsulated in the title of his wonderful book about the medium, Amusing Ourselves to Death. But McLuhan's insight into the significance of dominant media, expressed in another aphorism – "We shape our tools and afterwards our tools shape us" – always seemed profound and came to seem more and more so as television gave way to the internet and the networked world that we now inhabit.

The past few years, for example, have seen a series of angry and sometimes anguished debates about what a comprehensively networked ecosystem is doing to our children, our politics, our economies and even our brains. We wonder whether social networking might be fuelling political revolution, for example. And we ask if Google is making us stupid – or at any rate whether networked technology is reducing attention spans, devaluing memory and blurring the line between making online connections and forming real relationships. Over all of these contemporary debates looms the shadow of McLuhan, who now seems more insightful than ever.

He retains, however, the capacity to polarise opinion that he always had. Mention his name in polite academic conversation and you invariably see scholarly noses wrinkle in distaste. In part, this is because – although he was an impeccable scholar schooled in a Cambridge English faculty that included FR Leavis, IA Richards and Arthur Quiller-Couch – in his writings on media he affected an aloof, oracular, aphoristic style which enraged conventional academics. He always started his lectures with a joke and invited his students to ponder questions such as the semiotics of an advertisement for aspirin that featured a helmeted, jackbooted, scantily clad drum majorette. This is not the way to win friends and gain influence in academia.

McLuhan's big idea was to spot that the word "medium" has distinctly different meanings. The conventional one is that a medium is a channel for communicating information – which is why much discussion about media up to his time focused on the content that was being conveyed by print, radio and television. But there is another, equally significant, interpretation. To a biologist, a medium is an environment containing the nutrients in which tissue cultures – organisms – grow. Change the medium and you change the organisms. Our communications media likewise constitute the environment which sustains, nurtures – or constrains – our culture. And if the medium changes, then so does the culture. The medium is far more than the message, in other words. In fact, it's all we've got.