In a seminal booklet that he both designed and wrote, Carl Dair showed how in typography, as in music, harmony and contrast are the keys to composition.
The late Canadian typographer Carl Dair was one of the great typographic designers of the 1950s and 1960s, and he may have been the best of them all at explaining the nature of typography. In coordinated projects that he both wrote and designed, he managed to describe -- and show -- the ways in which manipulating and using type make typography happen.
Dair is the very epitome of what I mean when I say "typographer": someone who designs with type, not just a fancy typesetter, but someone who uses type, in all its variations, as the principle element of design. Since type carries meaning, the practice of typography requires a designer who cares about the words themselves. It requires someone who cares enough, and is skillful enough, to make the type express that meaning, rather than serve as simply eye-catching decoration.
Carl Dair's book "Design With Type" (originally published in 1952; revised and expanded in 1967) is deservedly still in print, even though the technology that he used and described has long been outdated. The practicalities of setting type in metal are no longer the practicalities we have to deal with; but the visual relationships between letters, which Dair showed and explained so graphically in his book, haven't changed at all. "Design With Type" is still one of the best handbooks available for learning how to do exactly what the title says: design with type.
At around the same time he was revising his book, Carl Dair was producing a series of six pamphlets for West Virginia Pulp and Paper (Westvaco), which he called "A Typographic Quest." Each booklet was, naturally, printed on Westvaco paper stock; like the lavish paper-company samples produced today, this series was meant to raise the profile of the manufacturer and encourage designers to think of Westvaco when specifying paper for their printing jobs. But these were quite modest productions: little saddlestitched booklets of about 30 pages, measuring 5-1/4 inches by 9, usually printed in two colors (the first one uses three colors throughout; the later ones are two-color, although the second color may change from sheet to sheet, with all three colors used together on the covers). The first "A Typographic Quest" was published in 1964; the sixth (and, as far as I know, final) came out in 1968, the year Carl Dair died. Since he was both writer and designer for the series, each of the booklets emerged as a wholly crafted object, dedicated to explaining one or another aspect of using type.
Dair first explains the "elements of harmony" (a consistent relationship between the black strokes of the letters on a page and the space around them; and any rules, frames, or decorations being similar in style to the type), then goes on to show seven different kinds of contrast. He emphasizes that in any kind of differentiation, it's important to make the contrast obvious -- not just a slight change, an almost imperceptible variation, but a really big, obvious difference between the contrasting elements.