media, typographers also are concerned with binding margins, paper selection, and printing methods when determining the correct color of the page. Principles of the typographic craft Three fundamental aspects of typography are legibility, readability, and aesthetics. Although in a non-technical sense "legible" and "readable" are often used synonymously, typographically they are separate but related concepts. Legibility and readability tend to support aesthetic aspects of a product. Legibility describes how easily individual characters can be distinguished from one another. It is described by Walter Tracy as "the quality of being decipherable and recognisable". For instance, if a "b" and an "h", or a "3" and an "8", are difficult to distinguish at small sizes, this is a problem of legibility. Typographers are concerned with legibility insofar as it is their job to select the correct font to use. Brush Script is an example of a font containing many characters that might be difficult to distinguish. The selection of cases influences the legibility of typography because using only uppercase letters (all-caps) reduces legibility. Readability refers to how easy it is to read the text as a whole, as opposed to the individual character recognition described by legibility. Use of margins, word and line spacing, and clear document structure all impact readability. Some fonts or font styles, for instance sans-serif fonts, are considered to have low readability and so are unsuited for large quantities of prose. Legibility "refers to perception" (being able to see as determined by physical limitations of the eye), and readability "refers to comprehension" (understanding the meaning). Good typographers and graphic designers aim to achieve excellence in both. "The typeface chosen should be legible. That is, it should be read without effort. Sometimes legibility is simply a matter of type size; more often, however, it is a matter of typeface design. Case selection always influences legibility. In general, typefaces that are true to the basic letterforms are more legible than typefaces that have been condensed, expanded, embellished, or abstracted. Studies of both legibility and readability have examined a wide range of factors including type size and type design, comparing serif vs. sans-serif type, roman type vs. oblique type and italic type, line length, line spacing, color contrast, the design of right-hand edge (for example, justification, straight right hand edge) vs. ragged right, and whether text is hyphenated. Justified copy must be adjusted tightly during typesetting to prevent loss of readability,