The Saxon infinitive ended in -an (_lufian_), and besides this there was a so-called gerundial form, _to lufigenne_. Besides these there were considerable differences in respect to particular words; but of these no notice is taken; the object being to indicate the differences between the _ancient_ and _modern_ stages of a language in respect to _grammatical structure_. 9. To bring about these changes a certain amount _of time_ is, of course, necessary; a condition which suggests the difficult question as to the _rate_ at which languages change. This is different for different languages; but as the investigation belongs to _general_ philology rather than to the particular history of the English language, it finds no place here. § 98. The extent, however, to which external causes may accelerate or retard philological changes, is _not_ foreign to our subject; the influence of the Norman Conquest, upon the previous Anglo-Saxon foundation, being a problem of some difficulty. At the first glance it seems to have been considerable, especially in the way of simplifying the grammar. Yet the accuracy of this view is by no means unequivocal. The reasons against it are as follows: a. In Friesland no such conquest took place. Yet the modern Frisian, as compared with the ancient, is nearly as simple in its grammatical structure, as the English is when compared with the Anglo-Saxon. b. In Norway, Sweden, and Denmark, no such conquest took place. Yet the modern Danish and Swedish, as compared with the Old Norse, are nearly as simple in their grammatical structure, as the English is, when compared with the Anglo-Saxon. The question requires more investigation than it has met with. An extract from Mr. Hallam's "History of Literature" closes the present section, and introduces the next.