3. For in many names that are aspirated in Greek we use _s_ instead of the aspiration. We have _sex_ for ἑξ, _septem_ for ἕπτα, and also the word _serpillum_ (thyme) for _herpillum_. _Octo_ is borrowed without change; they have ἔννεα, we _novem_; they δέκα, we _decem_. 4. _Decem_ is so-called from a Greek etymology, because it ties together and unites the numbers below it. For to tie together and unite is called among them δεσμεύειν.[242] [242] This derivation points to a soft _c_ in _decem_. Chapter 4. What numbers signify. 1. The science of number must not be despised. For in many passages of the holy scriptures it is manifest what great mystery they contain. For it is not said in vain in the praises of God: “Omnia in mensura et numero et pondere fecisti.” For the senarius, which is perfect in respect to its parts,[243] declares the perfection of the universe by a certain meaning of its number. In like manner, too, the forty days which Moses and Elias and the Lord himself fasted, are not understood without an understanding of number. [243] Six was regarded as a perfect number, because it is equal to the sum of all its factors. 3. So, too, other numbers appear in the holy scriptures whose natures none but experts in this art can wisely declare the meaning of. It is granted to us, too, to depend in some part upon the science of numbers, since we learn the hours by means of it, reckon the course of the months, and learn the time of the returning year. Through number, indeed, we are instructed in order not to be confounded. Take number from all things and all things perish. Take calculation from the world and all is enveloped in dark ignorance, nor can he who does not know the way to reckon be distinguished from the rest of the animals. Chapter 5. On the first division into _even_ and _odd_. 1. Number is divided into even and odd. Even number is divided into the following: evenly even, evenly uneven, and unevenly even, and unevenly uneven.[244] Odd number is divided into the following: prime and uncompounded, compounded, and a third class which comes between (_mediocris_) which in a certain way is prime and uncompounded, but in another way secondary and compounded. [244] _Pariter par, et pariter impar, et impariter par et impariter impar._ Since these all profess to be divisions of even number, the word odd is not used in the translation. 2. An even number is that which can be divided into two equal parts, as II, IV, VIII.[245] An odd number is that which cannot be divided into equal parts, there being one in the middle which is either too little or too much, as III, V, VII, IX, and so on. [245] To remind the reader of Isidore’s notation Roman numerals are kept wherever he used them. 3. Evenly even number is that which is divided equally into even number, until it comes to indivisible unity, as for example, LXIV has a half XXXII, this again XVI; XVI, VIII; VIII, IV; IV, II; II, I, which is single and indivisible.