Grammar schools. Are there any two words in the English language that produce more noise from a party conference? In Liverpool this week, Labour delegates are spitting the words like a teenager who has mistakenly taken a swig from a beer-can that was being used as an ashtray. The only time Jeremy Corbyn was uncomplicatedly cheered by his MPs was when the old boob called the proposal for more grammar schools "divisive and damaging".
Next week, in Birmingham, mention of grammar schools will again have a talismanic effect, only this time it will elicit cheers and ululations rather than groans. Yet, curiously, the words have become largely divorced from the proposals now being mooted. Both sets of activists are arguing about a 50-year-old reform of British education, not a contemporary one.
In the 1950s and 1960s, our school system was geared up to supply a manufacturing economy. If you passed your Eleven-Plus, you would be prepared for a white-collar job, and taught Latin and literature. If you failed it, you'd be taught metalwork. At least, that is how it is remembered today.
You don't have to be on the Left to think that there is something wrong with a state-enforced binary division of the entire population at eleven.
What most Conservatives want is a pluralist system, in which grammar schools take their place alongside technical schools, academies, faith schools and specialist schools of every kind. Just as there should be schools that concentrate on sport or music, so there should be schools that specialise in helping academically weak children and schools that specialise in helping academically gifted children.
Opponents of academic selection always talk of non-academic kids being "consigned" or "relegated" to non-grammar schools. They should take a closer look. I have visited a couple of technical schools as a constituency MEP and, believe me, they are way past metalwork. Their students are learning about 3D printing, electronics, precision engineering. Many of them will go on to far better-paid jobs than their literary contemporaries who become journalists.
What this row is really about is human nature. If you think that we all have comparable potential, and that how well we do is really down to what opportunities we're given, you will want all kids to be taught similarly. That was, indeed, the scientific consensus in the 1960s, when grammar schools and secondary moderns were merged into comprehensives. But, as Steven Pinker showed in his great study, The Blank Slate, the consensus has moved on. We now know that intelligence and other forms of aptitude are highly heritable.
Or, at least, scientists know it. Political discourse has lagged well behind academic discourse, and there are all sorts of things that are uncontroversial to behavioural psychologists but career-threatening to MPs. Making too much of innate differences is one of those things.
Paradoxically though, if the scientists are right, then having homogenous schools will produce more unequal outcomes than having diverse schools.
Some kids know from quite an early age that what they're really good at is, say, taking engines apart and reassembling them. If those kids are allowed to pursue that interest as the focus of their schooling, they will be happier and ultimately wealthier individuals than if they are made to sit through lessons on Chaucer. So, incidentally, the more academic kids will no longer have to share classrooms with those who don't want to be there. Everybody wins.
So why does Theresa May's proposal elicit such fury? Perhaps because, deep down, opponents of grammar schools are scared to admit that we are born with widely diverging talents. That would delegitimise too many of their other beliefs.
Daniel Hannan has been Conservative MEP for the South East of England since 1999, and is Secretary-General of the Alliance of European Conservatives and Reformists