For basic teaching purposes, there are four layers to the language that we use in the classroom: topic, context, function and form.
These give your learners the essential ‘what, where, why and how’ of your lesson. A lesson needs all four to make your lesson (and the language used) clear and engaging.
Topic – the ‘what’ of the language. What’s it about, in broad terms? Shopping, health, the internet, poetry? This should be a topic that your learners find interesting and relevant. Bonus points if you find it interesting too!
Context – the where and why of the language situation (and who!). Talking to a friend who’s looking for a job? That’s a context.
Function – the intent (or the why) of the language used. The function is simply the purpose of using the language. Why are we communicating? Every time we communicate, it’s for a reason. The function is that reason. If there were no reasons to communicate, then language would never have developed. In the above example, it could be giving advice on the best way to look for a job. Just ask yourself why a person is speaking. Nothing exists in a vacuum, and no language exists independently of meaning.
Form – this is what the language looks or sounds like. In other words, it’s the specific phonology, lexis or grammar you’re using. Are you using a rising or falling tone for question tags? Modals for giving advice?
Every lesson should have all four of these layers, and thinking about them before you write your lesson aims in detail can save you a lot of heartache. If it helps to remember, think of it as layers of an onion; topic is the overarching concept, the context is next, function is contained within the context, and the form is how the language looks or sounds like.
The good coursebook or syllabus will pick the topic, function and form out for you (and a great syllabus will have the context too!)
Oh, and in case you’re wondering where these four levels come from, I’ve adapted them from the six major levels of linguistics. I’ve simplified them a bit to make more sense in a classroom context, though. The original six major levels of linguistics are; pragmatics, semantics, syntax, morphology, phonology, phonetics.
Hope this is useful for you!