The study of architectural chronology and artistic identity is sometimes associated with the "Old" Art History that some believe was swept aside in the "theoretical turn" of the 1980s.  In fact, the pursuit of signs is both very ancient and very new.  In the passage down the length of the cathedral the visitor endowed with vision and memory cannot fail to notice similarities and differences: all the bays of the nave look very similar; come into the transept and choir and you notice differences: more light; the glazed triforium, different tracery forms.  What do these differences signify?  They could be construed as evidential signs of the passage of time and critical response--twenty-five years into construction, forms as originally conceived must have looked increasingly old fashioned.  Or they could be seen as conventional signs appropriate for expressing the hierarchy of spaces where the higher level of importance of the choir is expressed in more sumptuous architectural forms.  The viewer who becomes engaged in the pursuit of signs is Reading for the Plot (Peter Brooks, 1984)--pitting his wits to unscramble the underlying layers of meaning.  There is nothing old fashioned about this--it can become quite compulsive.  The most compelling evidential sign in the cathedral is fire damage concentrated in the south-west corner of the upper choir: we know from the written evidence that an arson fire took place in 1258.  Since a 1260 charter documents the identity of the master mason--Renaud de Cormont--there can be no doubt that Renaud was the master of the upper choir who initiated an architectural revolution.  Equally compelling as an architectural sign is the complete uniformity of the lower wall (the dado below the window still) down the length of the building to the base of the hemicycle: this must signify the work of the first master, Robert de Luzarches.  Our understanding of chronology and attribution is based upon reading such signs.