The economics of communicative circumstances have shaped the form of letters. For most of the time since the invention of writing about 5000 years ago, inscriptions primarily concerned authoritative orders, records, and knowledge. These circumstances imply much more frequent reading of inscriptions than writing them. Historically important examples of this balance between reading and writing are sacred texts such as the Bible.  Consistent with simple communicative economics, the forms chosen for letters are more closely associated with reading efficiency than writing efficiency.
Within a smaller historical scope, the shift in the form of the printed letter s suggests a similar pattern. Prior to about 1800, a “long s”, which looks like an f without the right part of the cross-bar, was used frequently in addition to the s used nearly exclusively today. The rules for the use of the long s were quite complicated. The demise of the long s is associated with the development of new typefaces and their rapid adoption. At the same time, an important communicative circumstances about 1800 was rapidly growing demand for new books driven by a rage for reading novels. While Benjamin Franklin apparently thought otherwise, not using the long s probably made for easier reading among the growing number of novel readers. Simplification of a script serves popularization of its use.
Size of the market also seems to correlate temporally with the demise of the long s. The demise of the long s in Spanish texts (about 1760) was earlier than its demise in French texts (about 1790) and English texts (about 1800). Including colonial markets, that order of demise is probable the same as the order of the size of the print markets for Spanish, French, and English texts in the late eighteenth century.
Growth of a market and size of a market are somewhat different demand factors. Growth of the reading population in the late eighteenth century plausibly correlates with less competence/experience in reading among customers actively choosing among books. Since supply-side scale economies weren’t significant relative to the total market size in late eighteenth-century printing, the significance of total print market size is harder to understand. Nonetheless, market circumstances, not just particular innovations or conventions, surely have been a major force in the development of letters.
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- selling via the title page
- explaining the long tale
- authors’ sex points to readers’ sex for early English novels
 Contemporary text messaging exemplifies a much lower reading/writing ratio.
 Scroll down toward the end of Andrew West’s awesome post on the long s to see his charts concerning the relevant trends in the use of the long s.
 Whether size of the market or growth of the market is a more propitious circumstance for a new business doesn’t have a general answer. Entrepreneurs today ponder and debate this sort of issue.