In typesetting it is a general rule to use one space character at a time (for example, see Webster’s Standard American Style Manual, p. 38). Thus, as a typesetting tool, the Macintosh differs from its earlier predecessors, especially the typewriter, where it is, for example, a general rule to type two consecutive spaces at the end of a sentence. Moreover, the Macintosh treats the width of the space character as variable. Thus, when justifying text, two spaces can be stretched to look like several spaces.
The OneSpace init’s purpose is to prevent users from typing more than one space in a row, especially by accident, thus preserving the standards of typesetting as well as the integrity of the Macintosh as a typesetting tool.
