Natural syntax. Here's an example of a piece of writing I did the other night about voice when I got myself steaming along. I think it has more than usual clarity and voice. Or at least I find something characteristic when I try to use it in my real draft. All my efforts to get it clear result in language that is more cramped and unclear and without voice. I noticed it when I was trying to follow it and borrow it and use it my real draft. Suddenly I had a sense that I was losing the juice in it. I even abandoned some of what I'd been writing on Wordstar and went to the ".bak" file to retrieve what I'd erased in trying to adapt it.
It sounds like an odd way to talk but really we do it all the time in face-to-face interactions. We listen to someone talk and make judgements about whether they really sound sincere; even people we don't know --even people on television: It is a common human perception to say: "I think that person is being sincere; or that person sounds genuine/fake." We know we are liable to be wrong about it--that it's an inference, but humans seem unwilling to refrain from making the judgement. This shows in cases where someone says, "She's trying to sound sincere but really she sounds fake." That is, it seems to be a human quality to listen to discourse and make judgements not only about the meaning of the words but about the relationship between the words and the person uttering them--even though, paradoxically, we are making judgements about the relationship between a and b when we have only a to go on.
You might say that we go on extra-discourse cues. But I doubt it. We can strip away those cues. That is, if we know the person well, we judge on the basis of knowing him in the past. But we do it with people we don't know (as with strangers, salesmen, future, new spouses of friends &etc. You could say we do it on visual cues, but in fact we do it over the phone and the radio. No visuals. We have tone of voice to judge from, it is true; but tone of voice is nothing but the person's "way of talking." When we see nothing but a text we don't have literal spoken tone of voice, so it is harder, but people still can't seem to resist doing it. For even in writing we still make these judgements based on "Way of writing." Here is the place to talk about increased emphasis on relation of words to writer with interest in voice. This is difference between speaking and writing. In speaking there is a tendency to pay a bit more attention to relation between words/speaker; In writing (since it gets along without a speaker--only the text is present--we may not even know who wrote it) there is a temptation to pay more attention to the words/meaning.