Porphyry observes that the first series of essays show the immaturity of youth—a period which he extends to what is generally considered the sufficiently ripe age of fifty-nine;—the second series the full-grown power of manhood; and the last the weakness of declining years. The truth is that his method of criticism, at least in this instance, was to judge of compositions as if their merit depended on their length, and perhaps also with reference to the circumstance whether their subject had or had not been previously talked over with himself. In point of fact, the earlier pieces include some of the very best things that Plotinus ever wrote; and, taking them in the order of their composition, they form a connected exposition of Neo-Platonic principles, to which nothing of importance was ever added. This we shall attempt to show in the most effectual manner possible by basing our own account of Neo-Platonism on an analysis of their contents; and we strongly recommend them to the attention of all Greek scholars who wish to make themselves acquainted with Plotinus at first hand, but have not leisure to wade through the whole of his works. It may also be mentioned that the last series of essays are distinguished by the popular character of their subjects rather than by any evidence of failing powers, one of them, that on Providence,[417] being remarkable for the vigour and eloquence of its style. By cutting up some of the longer essays into parts, Porphyry succeeded, much to his delight, in bringing the whole number up to fifty-four, which is a product of the two perfect numbers six and nine. He then divided them into six volumes, each containing nine books—the famous _Enneads_ of Plotinus. His principle of arrangement was to bring together the books in which similar subjects were discussed, placing the easier disquisitions first. This disposition has been adhered to by subsequent editors, with the single exception of Kirchhoff, who has printed the works of Plotinus according to the order in which they were written.[418] Porphyry’s scrupulous information has saved modern scholars an incalculable amount of trouble, but has not, apparently, earned all the gratitude it deserved, to judge by Zeller’s intimation that the chronological order of the separate pieces cannot even now be precisely determined.[419] Unfortunately, what could have been of priceless value in the case of Plato and Aristotle, is of comparatively small value in the case of Plotinus. His system must have been fully formed when he began to write, and the dates in our possession give no clue to the manner in which its leading principles were evolved.[420]