As to knowledge, I have often told you, and I am persuaded you are thoroughly convinced, how absolutely necessary it is to you, whatever your destination may be.  But as knowledge has a most extensive meaning, and as the life of man is not long enough to acquire, nor his mind capable of entertaining and digesting, all parts of knowledge, I will point out those to which you should particularly apply, and which, by application, you may make yourself perfect master of.  Classical knowledge, that is, Greek and Latin, is absolutely necessary for everybody; because everybody has agreed to think and to call it so.  And the word illiterate, in its common acceptation, means a man who is ignorant of those two languages.  You are by this time, I hope, pretty near master of both, so that a small part of the day dedicated to them, for two years more, will make you perfect in that study.  Rhetoric, logic, a little geometry, and a general notion of astronomy, must, in their turns, have their hours too; not that I desire you should be deep in any one of these; but it is fit you should know something of them all.  The knowledge more particularly useful and necessary for you, considering your destination, consists of modern languages, modern history, chronology, and geography, the laws of nations, and the ’jus publicum Imperii’.  You must absolutely speak all the modern Languages, as purely and correctly as the natives of the respective countries:  for whoever does not speak a language perfectly and easily, will never appear to advantage in conversation, nor treat with others in it upon equal terms.  As for French, you have it very well already; and must necessarily, from the universal usage of that language, know it better and better every day:  so that I am in no pain about that:  German, I suppose, you know pretty well by this time, and will be quite master of it before you leave Leipsig:  at least, I am sure you may.  Italian and Spanish will come in their turns, and, indeed, they are both so easy, to one who knows Latin and French, that neither of them will cost you much time or trouble.  Modern history, by which I mean particularly the history of the last three centuries, should be the object of your greatest and constant attention, especially those parts of it which relate more immediately to the great powers of Europe.  This study you will carefully connect with chronology and geography; that is, you will remark and retain the dates of every important event; and always read with the map by you, in which you will constantly look for every place mentioned:  this is the only way of retaining geography; for, though it is soon learned by the lump, yet, when only so learned, it is still sooner forgot.