"If the public does not understand scientifically accurate headings it should be taught. Do not lower the standard of scientific cataloging." To choose headings that should offend as little as possible these widely differing advisers, to steer a course between ultraconservatism and iconoclastic radicalism, was the difficult task that confronted me in undertaking the compilation of the new list of Subject headings. A special effort was made to formulate a principle that should govern the choice of adjective phrase; inversion; or noun, subdivided. Is it better to enter under Chemistry, Physiological, or Physiological chemistry? Under Psychology, Educational, or Educational psychology? Under Negro suffrage or Negroes--Suffrage? A strict rule for this sort of heading would be a boon to catalogers, but surely not to the users of the catalog. The average reader does not reason concerning the principles upon which the catalog is constructed. The fact that he today finds what he seeks entered under Chemistry, Organic, will not prevent his turning to Electric engineering rather than Engineering, Electric, tomorrow. The adoption of either form of entry to the exclusion of the others would lead to absurdities. Because it is satisfactory to subdivide Railroads, would it be desirable to abandon headings beginning Electric and substitute subdivisions of Electricity for Electric conductors, Electric lighting and Electric power? Or because Botany, Structural, is preferable to Structural botany, should we use Physics, Agricultural, instead of Agricultural physics? In the end, all efforts to frame the desired rule resolved themselves into something like this: It is necessary to use all three forms of heading; noun with subdivision, adjective phrase, and inversion. Each case must be decided upon its own merits, and that form used under which it is believed that the majority of readers will look,--the majority of readers in each particular library, be it understood. A university library will use many subdivisions because it is convenient for professors and students to have much of the material brought together under large subjects. A medical library will use few, if any, headings beginning Medical, because Medical is understood.