 These changes seem to be partly a consequence of developments in symbolic logic made by Peirce and his Johns Hopkins student, Oscar Mitchell, in the early 1880s. As is well known, during this time, and independently of Frege, Peirce and Mitchell developed quantification theory (see Peirce 1883, and W5. 162–191). An essential part of this development was the inclusion of singular propositions and individual variables for objects that cannot be picked out be definite descriptions. Peirce treated these non-general signs as indices, which in turn led him to identify the index as an essential part of logic. This made his earlier account of signs seem underdeveloped. (See, for instance, Short 2004, 219–222; Hookway 2000, 127–131; and Murphey 1961, 299–300). This appears to have led Peirce to take signs other than the symbol more seriously. In particular, it led Peirce to realize that some symbolic signs had distinctly indexical (that is non-general) features. Similarly, symbols with heavily iconic features, especially in mathematics (see Hookway 1985 Ch 6), were more important than he thought. What this meant, of course, was that the account of the 1860s was now woefully inadequate to the task of capturing the range of signs and signification that Peirce thought important for philosophy and logic.