I was recently priviledged to observe a discussion amongst typeophiles over which was better to use–kerning or tracking. It's a fair question, I think, because it illustrates that the two are similar enough in concept (though strikingly different in application) to cause a certain "blurring of the lines" between the two.
Both of them are all about letter spacing. Typographers speak of something called 'text color', and what they mean by this is that, when you look at a page of type, there is a general impression of a tone of darkness (I'm going to assume dark type on a light page). The overall letterspacing will have a bearing on this: tight spacing will cause the color to darken, and loose spacing will cause the color to lighten up.
I can see I'm getting a little ahead of myself here, so let's provide some definitions for the non-typophile:
Kerning refers to altering the spacing between only two letterforms. While the exact derivation of the term is unclear (one reference I use says the term stems from a German word for corner, which I find a little suspect), the kern itself is the area one letterform 'intrudes' into another letterform's space with. As an example, if you consider the word "Tower", the letterspacing between the majuscule T and the minuscule o looks more comfortable if one actually 'scoots' the o just a bit below the top cross-stroke of the T.
On the other hand, tracking refers to letterspacing over a range of letters–from a single word to parts of a sentence to whole sentences and paragraphs and beyond; in fact, another term for it is range kerning. Desipte being similar in concept–it has to do with spacing between the letterforms–it is not the same. Tracking is typically use to apply a standard amount of letterspacing over that range, and is not used with respect to any two individual letterforms. Tracking is usually termed "loose", for more space between than default, or "tight", for less.
Without using any examples, what may become evident here is that one isn't better than the other–one is more appropriate than the other. There are situations where tracking is a more appropriate tool than kerning. I'll illustrate.
A Situation That Calls for Kerning
Kerning is most appropriate when you are letterspacing very large letterforms, such as headlines, or any large text.
The reason that letterspacing is important is that uneven letterspacing tends to arrest the eye. Break open your favorite word processor (or if you have MSWord, for instance, get familiar with it–while they can't do layout, they're amazingly advanced on typography, once one gets to know them) and take some word (like Tower) that has an initial majuscule like T that un unascended minuscule "wants" to kern toward. Now make it real big–72 point or bigger.
If you've not touched the kerning, the program used the font metrics to determine the spacing. And you'll instantly be aware–even if only sublminially–that there's too much air in general between the letterforms, and the spacing of the letterforms themselves seem rather uneven. A typographer laying this out as a headline would put thier I-beam between each pair that looks like it needs it and kern them out (increase the space) or kern them in (decrease the space).
Kerning is best used on large letters, where individual tweaking can even out the spacing in headlines. When the spacing between large letters feels equal, the eye concentrates on the letterforms, and doesn't get 'hung up' on the space between
A Situation Calling for Tracking
Since kerning is most useful when the letterforms are big, it follows that tracking, if adjusted at all, might be most aprpos for letters at body text sizes–say, 10, 12, 13 points.
Consider any regular paragraph of text type, and think about the look of the letterspacing. At that size, the difference between irregularly spaced letters becomes very small, essentially unnoticeable to the untrained eye–which is most of everyone. Kerning is just not that essential.
However, when the eye does take in this text, it takes it in as a field and any overall differences are registered much more readily.
Tracking, at least when I've used it in this wise, is a tool for copyfitting. One of the challenges of the layout artist is to 'shoehorn' edited text (that's what we have editors for) into what is, most often, a predefined space. Adjusting tracking (along with adjusting leading and space before/after) is a quick way to make overset text fit into a space that's a little small.
The catch here is that you can vary it by just a little, but not too much; the eye will notice and attention will be called to the change, arresting your eye in the same way that uneven kerning on headlines will.
The key to the trick is to adjust tracking over a big range–not one sentence or one word, but one or more paragraphs as appropriate. The bigger the range, the smaller the amount of tracking per letterform pair is required. When you spread the change out, you have to change it less, and the final result will blend in better with the rest of the page, and not call attention to itself. The final look will be more professional.
It's a balancing act for the layout artist, and usually comes down to trial and error, but for the enlightened layout artist, it's an entirely doable thing.
And Now, To Summarize
Kerning occurs between two letters only, and is best used when the type is really large, as in headlines and subheads, but not text type.
Tracking is letterspacing over a range, and is best used when you're adjusting the type color to blend in with the rest of the layout, or copyfitting overset text. As Frederic Goudy said, "A man who would letterspace lower case would steal sheep", which has always meant to me that if you're kerning minuscules, you have a whole lot of time to waste, and are probably involved in other unsavory practices...like using MS Publisher.
It's not which is better...it's which is more appropriate.
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