WHO can say what order should be used to list adjectives in English? Mark Forsyth, in “The Elements of Eloquence”, describes it as: opinion, size, age, shape, colour, origin, material, purpose and then Noun. “So you can have a lovely little old rectangular green French silver whittling knife. But if you mess with that word order in the slightest you’ll sound like a maniac.” Mr Forsyth may have exaggerated how fixed adjective order is, but his little nugget is broadly true, and it has delighted people to examine something they didn’t know they knew.

Clearly, then, the discipline of linguistics needs a marketing overhaul, because this is exactly what linguistics consists of: describing the rules, many of them hidden and not obvious, of the human language ability. Given how eagerly word-nerds recently shared this tit-bit about adjective order on social media, the lecture-halls for linguistics classes should be crammed to the rafters.

Instead, as most linguists only too ruefully admit, upon confessing their profession at cocktail parties they tend to be told: “Oops, better watch my grammar around you.” Just as many psychologists moan that outsiders think the discipline is mainly about abnormal psychology, linguists haven’t sufficiently spread the word that they are not out to ban split infinitives or correct the misuse of “whom”. They consider themselves scientists (in a discipline that overlaps with psychology, cognitive science and others) in trying to learn how the human mind works.

They’ve found out many wonderful things about rules you know, but don’t know you know. For example, a question can be formed from a statement by turning the questioned element into a question-word (like “where”) and moving it to the front of a sentence. “Steve went to Toronto. Where did Steve go?” But that doesn’t work when the element in question is itself a clause: in “John wonders where Steve went to university” “went” can’t become “Where does John wonder that Steve went to university?” Everyone knows that the latter is awkward or even unacceptable, but very few people outside the world of linguistics know why. In fact, it took linguists themselves quite a while to work out the details.

There are hidden rules not just in grammar, but at every level of language production. Take pronunciation. The –s that marks a plural in English is pronounced differently depending on the previous consonants: if the consonant is “voiced” (ie, the vocal cords vibrate, as in “v”, “g” and “d”), then the –s is pronounced like a “z”. If the consonant is “unvoiced” (like “f”, “k” and “t”), then the –s is simply pronounced as an “s”. Every native English-speaker uses this rule every day. Children master it by three or four. But nobody is ever taught it, and almost nobody knows they know it.

Because linguists spend their careers trying to tease out what people actually do say and why, they get cross when people equate “grammar” with a host of rules that most people don’t actually observe. Take the so-called rule against ending sentences with a preposition. In fact, saying things like: “What are you talking about?” is deeply embedded in the grammar of English. “About what are you talking?” strikes real speakers of English as absurd. So it annoys linguists to no end to hear the latter “rule” associated with “grammar”, while the real, intricate grammar already embedded in the mind is ignored.

Sometimes our mental grammars don’t know what to do with unusual cases. Take the newish verb “to greenlight”, meaning to approve a project. What is its past tense? “Light” has the past tense “lit”. But some people go for “greenlighted” (Variety, a film-industry magazine, prefers this) whereas others go for “greenlit”. Why the confusion? It’s because “to greenlight” was formed anew from a noun phrase, “a green light”. One mental rule is that new words are always regular; hence “greenlighted”. But other people’s mental grammars see “greenlight” as a form of the verb “to light”, an existing irregular verb with the past tense “lit”; hence “greenlit”.

This implicit grammatical knowledge overwhelms, in its intricacy and depth, the relatively few rules that people must be consciously taught at school. But since the implicit stuff is hidden in plain sight, it gets overlooked. It is cheering to see that things like the adjective-order rule can go viral on social media. Perhaps it can make people more likely to associate “grammar” not with drudgery, but with fascinating self-discovery.