The opinion makers in philately held a serious discussion in the 1930s about what direction they hoped the hobby would go. By 1930 there was already a wide enough body of stamps issued for most countries that collectors were already beginning to lose interest in collecting collateral philatelic areas like cut squares, postal stationery, and revenues. The issue at hand was whether to preserve the complicated catalog listings or to bifurcate the hobby into more specialized traditional philately on the one hand and a simplified face different form of collecting on the other.
For United States stamps, this discussion played out in the “simplified” catalogs and albums that were issued in the 1930s and which you can still see today. The theory behind it was easy to understand. Most US collectors never really understand types of the classic US stamps, most never can tell the Bank Notes listings apart, and by 1930 most US collectors had more than enough to collect with Regular issues, Airmails, and Postage Dues for them to have much interest in the difficult Revenue issues with their paper types, and perf, imperf, and part perf varieties. The Simplified Movement was a nod toward reality. This was how most collectors collected anyway. Why not make it easier for them?
The Simplified Movement was first categorized as such in the 1930s, but the feeling behind it had always been present in the hobby. The first perforated stamps of the 1850s were simply perforated versions of the current imperf stamps, and there was considerable discussion in the journals of the time as to whether these constituted new collectible stamps or simply minor varieties of earlier items. The early album makers showed which side of the argument they came down on by making the spaces for these new perforated stamps in their albums so small that the stamps needed to have the perfs trimmed off by collectors in order to fit. Watermarks were more or less ignored by the earliest collectors, largely because, though some stamps were watermarked and some were not, there really were no watermark varieties of note until about 1900. If a stamp is issued only either watermarked or unwatermarked, it really is senseless to get out your tray to check. Collectors used to check for watermarks mostly to eliminate counterfeits as it is very unusual for a counterfeiter to go to the trouble of trying to duplicate the watermark on a stamp he has forged. Watermark trays only became a common tool in the United States about 1920 when the US Post Office switched from a double line watermark to a single line watermark to no watermark on our Washington-Franklin issues (and the watermark change was done because the double line watermark paper tended to shrink unevenly during printing and the changes were attempts to increase the quality of the printed stamps and had nothing to do with collectors). When shortly after this it was discovered that collectors could also tell faults and repairs by using a watermark tray, watermarking equipment became part of every collection.
Ironically, the Simplified debate has settled over the last thirty years, and, like many issues of this type, it was settled more by consensus than by debate. The plethora of new issues worldwide has made for a very simplified form of philately for those collectors who want it