In this sentence is summed up the whole mediaeval concept of the law of almsdeeds. Private property is allowed--is, in fact, necessary for human life--but on certain conditions. These imply that the possession of property belongs to the individual, but also that the use of it is not limited to him. The property is private, the use should be common. Indeed, it is only this common enjoyment which at all justifies private possession. It was as obvious then as now that there were inequalities in life, that one man was born to ease or wealth, or a great name, whereas another came into existence without any of these advantages, perhaps even hampered by positive disadvantages. Henry of Langenstein (1325-1397) in his famous _Tractatus de Contractibus_ (published among the works of Gerson at Cologne, 1484, tom. iv. fol. 188), draws out this variety of fortune and misfortune in a very detailed fashion, and puts before his reader example after example of what they were then likely to have seen. But all the while he has his reason for so doing. He acknowledges the fact, and proceeds from it to build up his own explanation of it. The world is filled with all these men in their differing circumstances. Now, to make life possible for them, he asserts that private property is necessary. He is very energetic in his insistence upon that point. Without private property he thinks that there will be continual strife in which might, and not right, will have the greater probability of success. But simultaneously, and as a corrective to the evils which private property of itself would cause there should be added to it the condition of common use. That is to say, that although I own what is mine, yet I should put no obstacle in the way of its reasonable use by others. This is, of course, really the ideal of Aristotle in his book of _Politics_, when he makes his reply to Plato's communism. In Plato's judgment, the republic should be governed in the reverse way, _Common property and private use_; he would really make this, which is a feature of monastic life, compulsory on all. But Aristotle, looking out on the world, an observer of human nature, a student of the human heart, sets up as more feasible, more practical, the phrase which the Middle Ages repeat, _Private property and common use_. The economics of a religious house are hardly of such a kind, thought the mediaevalists, as to suit the ways and fancies of this workaday world.