UI is visible. Type is visible.
In 1955, Beatrice Warde gave a presentation to the Typographer's Guild in London (now, the International Society of Typographic Design) which later became an essay titled: 'The Crystal Goblet, or Printing Should Be Invisible'.
A wonderful piece of writing in which Warde describes the role of typography – or rather the role of the designer - in printing. The general premise is that good typographic design shouldn't be seen.
When you listen to a song in a language you do not understand, part of your mind actually does fall asleep, leaving your quite separate aesthetic sensibilities to enjoy themselves unimpeded by your reasoning faculties. The fine arts do that; but that is not the purpose of printing. Type well used is invisible as type, just as the perfect talking voice is the unnoticed vehicle for the transmission of words, ideas.
Let's take that last point. Morgan Freeman has a memorable, wonderful speaking voice. One that adds colour and weight to the words. His words are not just audible, and understandable, but they are rich with personality. His voice adds to the words he speaks.
I disagree with Warde. Type should not always be invisible, it should be appropriate. Sometimes, it's a typeface's job to be overt, loud and suggestive, in order to communicate the content in the best way. But, yes, sometimes typography has to melt away into the background. To support the content and the reader. To help them.
On the web, because we're quite often presented with long-form text (and by that, I mean more than a few paragraphs), we get a little obsessed with body copy. Good typesetting of body copy should be like that of setting a novel; the type should disappear. But, not all typography is body copy, and to consider it in these narrow terms is to do the practice of typographic design a huge disfavour.
Whenever we design with words, we're designing with type. And words are not always long form paragraphs designed to be very easy on the eye. Sometimes it's a logotype, a button, a richly designed layout, a data table or form. The application of typographic design is just so broad that to say it all has to be invisible is to imply the goals of typographic design are the same across the board.
Legibility is a baseline requirement for typesetting anything. It's like edible food. It shouldn't really be a measure of what is good or not. Just like audibility and comprehension are baseline requirements for speech. There is more flavour in words; spoken or printed. There is more flavour in type, that if applied well, transcends content from being merely legible, to that of being pleasurable. After all, that's why we have different typefaces: each brings with it characteristics that flavour the words.
In my opinion, there is merit to visible typography because in the hands of a competent typographer, a text can truly sing. Not because they have left their mark out, but because they have worked their art on the words.
I agree which him completely. It's the difference between something edible and exquisite. The difference between average and better. Which is why all this invisible, reductionist UI approach is starting to grate on me a little because it suggests we have the same goal for all our work; to make it invisible. It's more complex than that. It's an over-simplistic measure of success that is put far more eloquently than in this post from Timo Arnall.
Of course, I say all of this under the one big caveat that, in typography, there are no rules. Just good decisions. But, let's make some decisions shall we? Not make everything invisible because, apparently, that's the way it should be.