An introduction that can only be understood after reading the whole chapter is no introduction at all.
That seems obvious, right? But how many times have you read the introduction to a chapter in a technical book and found yourself completely flummoxed by it, only to come back to it later and agree it makes perfect sense? Far too often, I'd wager, even if you're not conscious of it. But now that I've said it, you'll start to notice it more and more often....
This has always been a problem, but the much-acclaimed "democratising" effects of the internet are also "amateurising", and more and more people are attempting to write articles and books on technical topics without any real grounding in the principles of technical writing. Introdutions are one of the first things to suffer, and it is becoming all too common to see an introduction that talks about something in completely opaque terms, leaving the reader more confused than if there had been no introduction at all. The writer very often acknowledges this, commenting not to worry if you don't
My golden rule is simple:
Don't tell me something until you're ready to explain it properly. If I don't understand what you've said, you'd have been just as well saying nothing at all.
There are several factors that contribute to this problem, and some are more complex than others, so I'm going to focus on one problem alone just now: thematisation of new information confuses the reader.
What's thematisation of new information? I hear you cry. It's something I've just done to demonstrate the problem. I've been presenting a relatively coherent argument that you can follow without effort, even if you disagree with it. But then suddenly I threw in something your brain wasn't really ready to process, and you don't know what I'm talking about (unless you *do* know what I'm talking about, in which case just make believe for a while).
The "theme" of a clause or a sentence is (put simply) the first actual "thing" that the reader encounters (ie a noun phrase).
Consider the difference between:
Last week, John went to Paris.
John went to Paris last week.
In the first, we are talking about "last week", our theme, whereas in the second, we are talking about John. It's only a slight difference in emphasis, but it must be pretty important, otherwise we wouldn't go to the effort of maintaining the two different possible structures.
In the clause "thematisation of new information confuses the reader", the "theme" is "thematisation of new information".
I've started the clause with something most readers do not understand, and crucially I have done nothing to prepare them for it.
The conceptual gulf here is that the writer is fixated on the name of what they're trying to teach as a defining feature, rather than accepting that the name is arbitrary and effectively meaningless, and what we need to focus on is the concept and meaning.
Imagine you want to teach the idea of a biscuit tin. You've got a choice between:
"A metal container used to store biscuits is called a biscuit tin."and
"A biscuit tin is a metal container used to store biscuits."
The latter form assumes that the reader has encountered the term "biscuit tin" and is actively seeking its meaning, but the former introduces it the concept before sticking a label on it. It assumes we understand "metal container", "store" and "biscuits", but so does the other one. The first one, therefore, acts as a better introduction; the second is a dictionary entry, not copy for an instructional book.
A challenge for the reader: pick up a grammar book, any grammar book, and turn to the section on the subjunctive. How many times does the word "subjunctive" appear before the reader gets any real idea of the concept? And I'm not including "implies uncertainty or doubt", because that really isn't the meaning subjunctive in a great many languages. (EG in Spanish creo que... implies uncertainty, but it doesn't take the subjunctive.)
In my experience all the trickiest grammar points are provided with no adequate introduction in the vast majority of cases. When an introduction includes words to the effect of "don't worry if this is unclear, it will be explained later," I find myself wanting to ask the author why he didn't just leave it until he was ready to explain it properly.
Now I feel that my last sentence needs clarification: by explaining it properly I don't mean explaining it fully, because, of course, that's not what an introduction is supposed to do. An introduction can't and shouldn't give the full detail, but it should leave you with a rough notion of what the concept is, which can be refined as it goes.
Before I started properly on Scottish Gaelic, I read a great little book: Scottish Gaelic: a brief introduction (now republished as An Introduction to Scottish Gaelic). The book was an introduction. Each chapter was merely an introduction. The book didn't attempt to teach you anything in any depth, but to provide a broad overview of the concepts in the language. It's hard to say exactly how much of an effect it had on my learning, but I certainly didn't feel like I struggled with many of the concepts when I finally came round to actually learning how to use them "in anger".
I've read several internet language learners say they like to use grammar books this way -- read through without "learning" per se, just to get a feel for the overall "shape" of the language before starting to study in earnest, so it's a shame there aren't more books written in this style.
The introduction author has two great enemies.
The first is precision. No-one wants to write things that are wrong, and any simple explanation is prone to being cut down by pedantry, which ends up leading many to start with a dry technical description, which doesn't really help the reader to understand.
The second enemy is the contents page.
Think about it: the textbook has never managed to supplant lectures as the main source of study, despite being cheaper than face-to-face lessons and far more readily available. And what do all textbooks have in common? Contents pages.
What... you expected a more in-depth argument than that? Correlation isn't good enough for you? Well then, try this on for causation:
What do you get on a contents page? Quite often a single noun phrase. "The nominal group." "The subjunctive mood." "Hydrostatic load." "Currying functions." Before you even turn to the first page of the chapter you're bombarded with arbitrary, undefined terms. All new information, all theme; nothing that actually means anything.
I believe that this predisposes people to write bad introductions, because it makes them act as if the reader is looking for a definition of a given term, when often nothing could be further from the truth: the term given is merely a label of convenience to summarise a body of knowledge that the writer hopes to impart to the reader.
But now the word's up there in bold type and there's no getting away from it. It could be ignored, but wouldn't you feel a little silly actively avoiding the word used in the title of the chapter for the first page or two? The title has poisoned the chapter.
OK, I'm exaggerating grossly here. Not all books have bad introductions. Some books have meaningful chapter titles rather than simply throwing the jargon in there. But there's something about the format that encourages thinking this way, and it's something that bears conscious consideration....