This paper discusses the relation between letters and numbers in the case of ancient Greek and, other writing systems and, supports that priority must be given to the numbers, that is to say the use of letters of the alphabet was constrained, by the necessities of mathematics. In the case of Ancient Greece the ‘24 letters of the alphabet’ plus ‘3 additional signs’ were used to notate the numbers. These 27 signs formed the three enneads of the Greek Numeral System, (...) which was in use in Eastern Mediterranean and parts of Europe for almost 2,000 years. So, the 24 letter-signs were also digit-signs. The arithmetic use of letters is considered by epigraphologists and Hellenists a later development, occurring two or three centuries after the invention of the Greek alphabet. This paper supports that, from the very beginning, the alphabet should, have had, 27 signs in order to meet the needs of mathematics, that is to meet the necessity of using the enneads of the Egyptian numeral system, which probably was transferred, to Greeks via the Semitic writing system. This hypothesis is based, on the contradictions which arise between the choice of signs and their use, from ancient Greek ‘Logistikē’, from archaeological finds and from the examples of other writing systems, which were also created so as to serve the needs of mathematics — namely Hebrew, Arabic, Coptic, Armenian, Georgian, and, other alphabets. Consequently, the alphabet should, not be considered, as a secondary system of signs, which was created, in order to record, the spoken word, but as a subset of a broader semiotic system that attempts to express human Reason in general. (shrink)