My text may be said to be founded on that of Halm which appeared in the edition of Cicero's philosophical works published in 1861 under the editorship of Baiter and Halm as a continuation of Orelli's second edition of Cicero's works, which was interrupted by the death of that editor. I have never however allowed one of Halm's readings to pass without carefully weighing the evidence he presents; and I have also studied all original criticisms upon the text to which I could obtain access. The result is a text which lies considerably nearer the MSS. than that of Halm. My obligations other than those to Halm are sufficiently acknowledged in my notes; the chief are to Madvig's little book entitled _Emendationes ad Ciceronis libros Philosophicos_, published in 1825 at Copenhagen, but never, I believe, reprinted, and to Baiter's text in the edition of Cicero's works by himself and Kayser. In a very few passages I have introduced emendations of my own, and that only where the conjecttires of other Editors seemed to me to depart too widely from the MSS. If any apology be needed for discussing, even sparingly, in the notes, questions of textual criticism, I may say that I have done so from a conviction that the very excellence of the texts now in use is depriving a Classical training of a great deal of its old educational value. The judgment was better cultivated when the student had to fight his way through bad texts to the author's meaning and to a mastery of the Latin tongue. The acceptance of results without a knowledge of the processes by which they are obtained is worthless for the purposes of education, which is thus made to rest on memory alone. I have therefore done my best to place before the reader the arguments for and against different readings in the most important places where the text is doubtful.