So, a lexical syllabus would be one based on lexis, not structures or functions. And that this makes sense being that lexis is highly correlational. there's not smoke without...that other thing. Lewis argues that lexis is not vocabulary. Vocab, he believes, is high content nouns and low informational content prepositions. Learning these isolated or in semantic fields is a mistake he believes.
Lexis is viscorous, like a polycarbon, each molecule is chained up and wrapped around others. Let's have a look at how vocab and lexis is different, what lexis is composed of, and some characteristics of lexis.
Importantly, lexical units are not just words. They can be words, but they also include collocations, polywords and certain idiomatic phrases. So how come some words are lexical units and some are not?
Well, language, believe it or not, is not individually defined, but socially defined, and we as speaking communities prefer to hear language "done right". Doing language right is not a matter of referencing some generative grammar rules, but instead reading the right phrases from the phrase book.
There are many ways of getting your meaning across, but we often prefer to use a handful of the possible (including the more literal) options. This is because language is a social institution. We participate within it, choosing to interact within it according to norms and conventions that are expected, where the speaker is penalised for deviating from these rules.
Say you're at the dinner table and you want some salt or pepper or balsamic vinegar of some soya milk or whatever the hell it is, and you ask your friend, who's standing, to pass you that thing that you can't quite decide what it is, so you say...."pass us the.. / could you pass me the... / throw us the.... / would you mind....", but interestingly, you wouldn't say "give me the / get me the / hand over the / the "widget" please.
Even though these are simpler, they are just not done.
So, we often may often prefer idiomatic phrases to literal ones where the meaning is derived not from the lexis itself but its place in the discourse. this is lexis: the preferred, non-literal, pieces of language we use to communicate with other people rather than just...a list of nouns.
Lewis wants to avoid teaching vocabulary as just decontextualised nouns. He wants to present high content words in true nature, how they're actually used in relation to each other and low context words. teaching a list of nouns and collocations and functions as well as a structural syllabus isn't enough. Language should not be broken down and atomised but presented in its true natural communicative glory, students should see lexis, and the specific forms it takes, it's co-text, in relation to its pragmatic role in a dialogue and its intended meaning. it should be mastered as a whole, then only later, when it is familiar with the learner, can hypothesising and experimentation begin.
O - H - E is the watch-word. Not P P P. But more essentially, try not to break down language into its consituent parts. It's unhelpful, it's like showing someone a glass of water and saying, look, i got this from a river, and hoping observing the water will put across what the river was actually like.