A chemist who either discussed his subject, or worked in his laboratory, on the assumption that all elements were equal, or that matter was composed of single homogeneous units called “molecules,” would not remain long in his profession. Force of ridicule, or of some even more drastic happening, would remove him. But the economics of many practical and pressing problems is continually bedevilled by discussions, and even on occasion policies, which involve a sort of stubborn simplification quite unworried by the facts. It is certainly understandable that, in the field of housing, this complaint has arisen frequently from those who have tried to deal with the subject from a social rather than a particularist viewpoint, and in its full dimensions rather than within the limits of some familiar phase. In the effort to get low-rent housing into its proper perspective, there are two obstacles which are particularly troublesome. One is the assumption that all housing “units” are the same, the kind of view which leads to the belief that “one thousand houses built” is the same contribution to national need, no matter what kind of houses they may be. The other is the argument or belief which really involves the assumption that peoples' incomes are broadly equal, and all comfortably above the average. The most frequent version is that most people, or at least a majority, can afford to own their own home, or should be encouraged to do so. A more valid but troublesome one in its “all-or-nothing” form is that cheapening the cost of construction is the “real” problem; and there are other variants. Another version, less frequently heard in these days of pressure, is that people live in slums because they like it.