FRANÇOISE DESBORDES: A study of the formula «addition, subtraction, mutation, metathesis» in ancient theoretical texts. Study of the formula and its variants in ancient theoretical texts. Origin of the linear formula and model of the operations that apply to writing. Ellipsis as a «gap» with respect to «sermo rectus». Recurrence of the model at various levels: theories of spelling, barbarism, solecism, rhetorical «figures», and the role played by ellipsis in syntaxe This study also includes a terminological clarification and deals with the difficulties that result from the use of the formula when the items concerned are words. Thinking out the implications that surround the notion of ellipsis in antiquity is not pointless for modern Iinguistics since the notion is still used in a way which does not seem ta be basically different.