Allograph

Allography, from the Greek for "other writing", has several meanings which all relate to how words and sounds are written down.

An allograph may be the opposite of an autograph – i.e. a person's words or name (signature) written by someone else.

In graphemics, the term allograph denotes any glyphs that are considered variants of a letter or other grapheme, like a number or punctuation. An obvious example in English (and many other writing systems) is the distinction between uppercase and lowercase letters. Allographs can vary vastly, without affecting the underlying identity of the grapheme. Even if the word "cat" is rendered as "cAt", it remains recognizable as the sequence of the three graphemes ‹c›, ‹a›, ‹t›. Thus, if a group of individual glyphs (shapes that may or may not represent the same letter) are allographs (they do represent the same letter), they all represent a single grapheme (a single instance of the smallest unit of writing).

Letters and other graphemes can also have huge variations that may be missed by many readers. The letter g, for example, has two common forms (glyphs) in different typefaces, and an enormous variety in people's handwriting. A positional example of allography is the so-called long s, a symbol which was once a widely used non-final allograph of the lowercase letter s. A grapheme variant can acquire a separate meaning in a specialized writing system. Several such variants have distinct code points in Unicode and so ceased to be allographs for some applications.

The fact that handwritten allographs differ so widely from person to person, and even from day to day with the same person, means that handwriting recognition software is enormously complicated.

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