A Mark Built by Doubling

Brahmi writes the mark for this vowel by doubling the element used for e, so the shape on the page records the analysis the phoneticians gave the sound: one step further along the same series, written as one more of the same stroke. That is a general habit of the script rather than a single convenience. The mark for au is built on the mark for o in the same way, and the four compound vowels form a family of related shapes rather than four unrelated signs. A writing system that encodes its own phonetic analysis in the shapes is unusual, and it is one of the features that makes the Brahmi vowel series worth studying as a designed object.

The habit does not survive intact into every descendant. Some of the later scripts keep the doubling plainly visible, some fuse the two elements into a single stroke, and some rebuild the sign around a different base entirely, so the family resemblance among the compound vowels is clearer in the parent script than in several of its children. Tracking where the doubling was kept and where it was lost is one of the ordinary comparisons of Indian palaeography, and it groups the descendant scripts in ways that do not always match how they are grouped by geography.