History of sentence spacing

The history of sentence spacing is the evolution of sentence spacing conventions from the introduction of movable type in Europe by Johannes Gutenberg to the present day.

Typesetting in all European languages enjoys a long tradition of using spaces of varying widths for the express purpose of enhancing readability. American, English, French, and other European typesetters' style guides—also known as printers' rules—specified spacing rules which were all essentially identical from the 18th century onwards. Early English language guides by Jacobi in the UK^[1] and MacKellar, Harpel, Bishop, and De Vinne in the US^[2] specified that sentences would be separated by more space than that of a normal word space. Spaces between sentences were to be em-spaced, and words would normally be 1/3 em-spaced, or occasionally 1/2 em-spaced (see the illustration to the right). This remained standard for quite some time.

MacKellar's The American Printer was the dominant language style guide in the US at the time and ran to at least 17 editions between 1866 and 1893, and De Vinne's The Practice of Typography was the undisputed global authority on English-language typesetting style from 1901 until well past Dowding's first formal alternative spacing suggestion in the mid-1950s^{[citation needed]}. Both the American and the UK style guides also specified that spaces should be inserted between punctuation and text. The MacKellar guide described these as hair spaces but itself used a much wider space than was then commonly regarded as a hair space.^[2] Spaces following words or punctuation were subject to line breaks, and spaces between words and closely associated punctuation were non-breaking. Additionally, spaces were (and still are today) varied proportionally in width when justifying lines, originally by hand, later by machine, now usually by software.

The spacing differences between traditional typesetting and modern conventional printing standards are easily observed by comparing two different versions of the same book, from the Mabinogion:

1. 1894: the Badger-in-the-bag game—traditional typesetting spacing rules: a single enlarged em-space between sentences
2. 1999: the Badger-in-the-bag game—modern mass-production commercial printing: a single word space between sentences

The 1999 example demonstrates the current convention for published work. The 1894 version demonstrates thin-spaced words but em-spaced sentences. It also demonstrates spaces around punctuation according to the rules above and equivalent to French typesetting today.