Last year, Nick Carr wrote a forceful article for the Atlantic magazine, arguing that Google was making us stupid. It's not just Google, of course, but the whole chaotic wave of technology that seems to be sweeping us into the future, surrounded and sometimes battered by the flotsam and wreckage of old certainties. And that was before Twitter hit the big time.

This month's issue of the magazine has a riposte by Jamais Cascio, who has spent a long time in the future, and who believes that technology has already made us enormously smarter. This won't happen, he says, because of the kind of dramatic stuff that crops up in conventional speculation, like digital brain implants. No, it is all around us already, in the web and all the things that it lets us do. The trouble is the things the web lets us do aren't actually all that intelligent. Cascio gets round this by redefining intelligence as "fluid".

Fluid intelligence, he says, is defined as: "The ability to find meaning in confusion and to solve new problems, independent of acquired knowledge. Fluid intelligence doesn't look much like the capacity to memorise and recite facts, the skills that people have traditionally associated with brainpower. [But] the information sea isn't going to dry up, and relying on cognitive habits evolved and perfected in an era of limited information flow – and limited information access – is futile. Strengthening our fluid intelligence is the only viable approach to navigating the age of constant connectivity." We've heard this before, and more pithily, when the borg queen said resistance was futile. But it doesn't have to be boiled down. You can get a detailed version into something scarcely longer than a tweet: "Sure, we can't read or write complicated sentences, and nobody can remember anything for longer than it takes to cut and paste but what does this matter when we have 'fluid intelligence?'"

This kind of optimism depends on a number of assumptions and stereotypes. It depends on an absurd view of intelligence, as if there were nothing between automation and intuition. Of course there are circumstances in which following the old procedural rules no longer work. But they are the times when we need most to cultivate the habits of disciplined thought, to master the confusion. This kind of problem crops up constantly in armies, where disciplined and stereotyped behaviour is both essential and sometimes lethal. Armies value two qualities in their officers besides leadership: initiative, and the capacity to recognise the problems that need a new kind of solution – and distinguish them from those that don't. Those are the skills that do the jobs that "fluid intelligence" is supposed to and neither skill depends on computer networks nor is much nourished by them.

The real problem with Cascio's optimism is deeper and appears in his justified dismissal of most futuristic hype about brain implants and the like. Who would put the 2009 chip in their brain when in three years competitors would have upgraded to the 2012 version? This is a good question, but it should be carried further. We don't have to put chips in our brain to change the ways we think. All we need do is form new habits, and this in fact is something that we can't avoid doing, for good and ill. Children brought up in front of the television have in effect rechipped their brains compared to those brought up only with books; and children brought up in front of computers are different again.

It follows that if we've been dumbed down by technology, we may be unable to recognise it. Students copying from Wikipedia think they are smarter than their parents, in the same way drunks think they are able to drive. But it's important here to worry about the right things. It's not the technology that damages our ability to think. It's the habits of mind that technology promotes. The habits of disciplined, careful thought that linear reading promotes are more useful for understanding a changing world than the ability to pay superficial attention to five different streams of information. I don't think computers make it more difficult. It has always been difficult. But if they allow us to pretend we don't need it any more, then they are really helping us to become a lot more stupid, fluidly or not.