 Sometimes only the first part of the quote is recalled, and that might raise the question whether he did not notice the great differences: for instance that natural languages develop without an a priori set of rules whereas artificial languages have an explicit syntax and are designed for a special purpose. But the quote as a whole expresses clearly what Montague meant by ‘no important theoretical difference’; the ‘single natural and mathematically precise theory’ which he aimed at, is presented in his paper ‘Universal Grammar’ (Montague 1970c). He became most well-known after the appearance of Montague 1973, in which the theory is applied to some phenomena which were discussed intensively in the philosophical literature of those days.