(a) About fonts: nature and legibility

Before introducing the typeface families and explaining matters such as line spacing, it is helpful to introduce the working vocabulary of typeface designers (and typesetters). First, a font was originally referred to as a typeface of a certain size and style (and a style is a condensed, light, bold or other variant of the main typeface). Now that typefaces are not cut from wood or cast from lead anymore, the terminology has become a bit clouded since font is now synonymously used for all typefaces.

Font properties. When two fonts are printed in the same size, one often looks bigger than the other. Bigger x-heights make a typeface appear larger. Differences in line weight and character width also affect the fonts’ perceived size. What do they mean, x-height, small-caps, serifs, stem, ascender and descender?

Small caps are in a league of their own: they are not upper-case letters of a smaller size, but small capitals designed to match optically with lower-case letters. They are slightly higher than the x-height (and about 82 percent of the moderate capital’s height) and about 87 percent of the moderate capital’s width. In contracts, small caps can be used for all-caps party names: asml, tnt, bp, basf, bmw, sap, nxp, lvmh. Do not overuse small caps.

Legibility and readability. A decisive factor for selecting a font is its ‘legibility’. Many fonts are designed to convey a sense of novelty or fanciness, properties that are irrelevant and even undesirable for contracts, prospectuses or legal advice.
Legibility is influenced by various factors, some of which are more important than others. A factor improving legibility is serifs, which harmoniously link letters to each other. On computer screens, however, sans serifs appear to be more legible. Also, over time, the sans serif font designs have been improved to reduce the impression that the stems of two adjacent letters blend. A remarkable aspect affecting legibility is the design of the upper half of the font; whilst the upper part remains relatively legible when removing the lower half, the opposite is certainly not true. (Try it yourself with a ruler.)
In addition to the concept of ‘legibility’, which largely relates to font properties, is that of ‘readability’, which relates to texts as a whole. Readability not only deals with semantics, grammatical structuring and drafting style, it also relates to the typography and use of fonts in texts, line spacing and alignment.