Robert Bringhurst, The Elements of Typographic Style, (p.43–44):

The typographic terminology is telling. Isolated lines created when paragraphs begin on the last line of a page are known as orphans. They have no past, but they do have a future, and they need not trouble the typographer. The stub-ends left when paragraphs end on the first line of a page are called widows. They have a past but not a future, and they look foreshortened and forlorn. It is the custom — in most, if not all, the world’s typographic cultures — to give them one additional line for company.

In his excellent essay, “The New Web Typography,” Robin Rendle defines three principles of web typography:

1. We must prioritise the text over the font, or semantics over style.
2. We ought to use and/or make tools that reveal the consequences of typographic decisions.
3. We should acknowledge that web typography is only as strong as its weakest point.

Must-read for designers.

Robyn Blakeman, The Bare Bones of Advertising Print Design, (p.44):

Effective use of white space is the key to an organized design that enhances readability and legibility. Readability is achieved when a viewer can read an ad at a glance. Legibility refers to whether, in that short look, they understood the message.

Adrian Frutiger, Adrian Frutiger Typefaces: The Complete Work, (p.65):

I must stress, however, that most harmonious line is not automatically the most legible one. Only the diversity of individual letters with ascenders and descenders, with straight or diagonal strokes or curves guarantees the best legibility.

Erik Spiekermann, Stop Stealing Sheep & Find Out How Type Works, Third Edition, (p.179):

[W]hen you pick a typeface for text in small sizes that is meant to be read on screen, remember Garamond. Don’t sacrifice esthetics for practicality. Pick a typeface that has character and strength. Basically, the models which survived 500 years will look good on screens today.

Jeff Johnson, Designing with the Mind in Mind, (p.69):

• In alphabetic scripts, patterns of characters form morphemes, which we learn to recognize as packets of meaning—for example, “farm,” “tax,” “-ed,” and “-ing” are morphemes in English.
• Morphemes combine to form patterns that we recognize as words—for example, “farm,” “tax,” “-ed,” and “-ing” can be combined to form the words “farm,” “farmed,” “farming,” “tax,” “taxed,” and “taxing.” Even ideographic scripts include symbols that serve as morphemes or modifiers of meaning rather than as words or concepts.

The following references are from Richard Hendel, On Book Design:

If printing is the black art, book design may be the invisible one. (p.1)

The more mundane the object (a pencil, a book), the less we think about its design. The more often we use it, the less we think about how it came to be. But the simplest object often has very complicated specification for making it.

Book design us, indeed, an arcane subject. We need context to understand it. Knowing a technical vocabulary does not provide that context; rather, we need to be aware of the specific problems that book designers must consider as they work. (p.1)

Among the many ways a book can be designed there are three main approaches:

1. typography that is neutral as possible, suggesting no time or place
2. allusive typography, which is purposely gives flavor of an earlier time
3. new typography, which presents a text in a unique way. (p.12)

Although some designers claim to be able to design a book in all its essentials before choosing a typeface, I cannot. The typeface I use influences so many other parts of the page that until I can settle on which to use, I am unable to carry on. It is the basis for everything else. Choosing a typeface can be the most vexing, infuriating, time-consuming, and pleasurable part of designing a book. (p.35–36)

The author’s words are the heart of book design. To solve the design problem for a book, a designer needs to know both what an author is saying (what a book is about) and how it is being said (the actual words being used). (p.33)

Assuming I can understand the subject of the book, I usually read the introduction or first chapter, and I read some of every few pages to get a sense of the author’s style. The author’s vocabulary often dictates the typeface I use. (p.33)

Lynne Watts and John Nisbet, Legibility in Children’s Books, (p.19):

Legibility as a priority may suffer; but by knowing precisely what diminishes legibility, the designer is in a better position to decide how far reading efficiency should be reduced for considerations of impact, visual experience, ‘atmosphere’, etc.

Capital letters (p.21):

Research studies have shown that children are more familiar with capital letters than with lower case letters. They are able to name correctly more capital letters than lower case, to perceive capitals more easily and to experience less confusion in differentiating between individual letters.

Clarity vs. legibility (p.33):

The geometric design of modern typefaces is appreciated by many designers for its clarity and symmetry. However clarity and legibility may be in conflict.

Type size (p.49):

A type size should be large enough to enable ease of letter discrimination, but small enough to encourage word recognition rather than letter recognition. This would preclude the use of a type size larger than 18 points. Generous leading would appear appropriate for children in the early grades where perception and spatial difficulties are commonly found.

Ruari McLean, True to Type, (Author’s preface):

Type is only a tool. It is one method of communication. Typography is the art, or skill, of using that tool in the most useful way for the purpose intended. The typographer is the person who exercises that art, or skill.

The words do not necessarily have to be read easily, but they have to be read unmistakably, and in the right frame of mind, by the right people.

It is the unique fascination of the typographer’s problem that it involves both design and literature. The designer who has no feeling for words will never make a good typographer.

A piece of typography may be ‘beautiful’: that is to say, pleasing to the eye. But to whose eye? If it is not pleasing to the eye of the customers it is intended to please, it is not a well-design job.

Daniel Burkely Updike, In the Day’s Work, writes:

A good test of spacing is to hold a printed page upside down, when, the sense of the words not being caught, the eye more readily perceives whether the spacing of the page is even or not.