You only get up to 14 areas of expertise.

Edit: for updated thinking see Theory of the day 3

For most of my adult life I’ve believed that you don’t get an opinion that anyone needs to care about unless you really know about something. You can vaguely think something, you can suspect something, you can tentatively offer something, but you don’t get to assume anyone will agree with you, or get to try to persuade someone of your opinion, unless you really know what you’re talking about.

I’m sure you’ve all been on the bad end of this knowledge-opinion mismatch: people who explain your job to you; the young-people-today rant; the political ‘expert’ who crumbles into a sulking pile of insults as soon as you ask any question more penetrating than ‘how did you become so brilliantly knowledgeable?’

And today’s extension of the theory is to quantify this: let’s assume that your expertise-refining life begins at 10 (I was tempted to say 15, but I knew A LOT about Gilbert and Sullivan by the time I was 15) and finishes at 80. When juggled with a job and everything else life throws, to get to a stage where your opinion is worth something to strangers takes about 5 years. So, depending on the age of the person, they get to be expert in up to 14 things. Only 14. And that’s only if a person has actively worked at developing that expertise in each 5-year period – the saying that you can live 80 years or one year 80 times is one of those annoying clichés that annoy me even more by being true, and this is especially true for developing expertise.

I don’t mean to be exclusionary or elitist about these areas of expertise: it could be an encyclopaedic knowledge of Star Trek, or a deep understanding of the psychology of Phil Mitchell from EastEnders, or the magic of how to get your youngest child to stop screaming. All of these are highly valuable areas of knowledge, particularly if I’m in a restaurant with your child.

And there are the wonderful people – whom I envy and idolise – who disappear down the rabbit hole of one particular academic area, occasionally emerging to announce a new discovery in the multiverse theory, and then aren’t seen again for years. These people who think that a breadth of knowledge means knowing about both the interstellar medium and the cosmic microwave background. If your 14 areas of expertise are knowing the first names of 14 individual atoms, I salute you.

As well as a number, I also give to you a way of validating that standard: you can be considered an expert in something if:

You have a good knowledge of the facts in the area and wouldn’t embarrass yourself if this was your specialist subject on Mastermind
You know and can apply the main theories of the field to new knowledge
And the ultimate test: you can explain your theories clearly and entertainingly enough to interest a ten-year-old.

And, as all my theories do, this gives us a clear and easy way to make the world better. Each person you talk to should present their list of areas of expertise before making any statement about anything factual in the world, and if the statement is about anything not on the list you can pat them on the head and move on. And if you doubt their actual level of expertise and want to test it, a ten-year-old is never far away.

(Incidentally, this does suggest that there’s a good TV series to be had from anyone who wanted to gain official certification on their area of expertise. Call me, BBC!)

But this also gives you – yes, you – something to aim for: it’s easy as life progresses to settle back on your existing expertise and to think that’s enough. However, the existence of the list implies that you should be developing a whole new area of expertise every five years. It also suggests that society should support people in developing their expertise. Adult education is child education’s neglected aunt – currently society’s obligation to our learning stops at the age of 18, which seems like a terrible waste of potential when your best friend could be studying Spanish, or your mother learning to code, or I could finally master the perfect lasagna. Think of what we could be if we learnt something entirely new every 5 years – in my case, quite a bit fatter, but perhaps happier and wiser too.