And even though this development deteriorated into an academic matter right away, the topic itself always managed to remain crucially significant. The textbooks of the Greek and Latin grammarians were schoolbooks in the West for over a thousand years. We know that these were anything but weak and petty times.
We are asking about the word form that the Latins call the infinitivus. The negative expression, modus infinitivus verbi, already points to a modus finitus, a mode of limitedness and definiteness in verbal meaning. Now what is the Greek prototype for this distinction? What the Roman grammarians designate with the bland expression modus the Greeks call ἔγκλισις, an inclining to the side. This word moves in the same direction of meaning as another Greek word indicating grammatical form. We know this word, πτῶσις, better in its Latin translation: casus, case, in the sense of the inflection of the noun. But to begin with, πτῶσις designates any kind of inflection of the fundamental form (deviation, declension), not only in substantives but also in verbs. Only after the difference between these word forms had been more clearly worked out were the inflections that belong to them also designated with separate terms. The inflection of the noun is called πτῶσις (casus); that of the verb is called ἔγκλισις (declinatio).Now how do these two terms πτῶσις and ἔγκλισις come into use in the examination of language and its inflections? Language is obviously taken as another thing that is, as a being among others. The way in which the Greeks generally understood beings in their Being must have made itself felt in the conception and definition of language. Only on this basis can we grasp these terms, which, as modus and casus, have long since become hackneyed labels that tell us nothing.
In this lecture course, we constantly return to the Greek conception of Being because this conception, though entirely flattened out and rendered unrecognizable, is the conception that still rules even today in the West