Admitting, as we are compelled by the facts to admit, that there exist many undoubted examples of skew chancels, we next look for an interpretation. Two schools of thought, the symbolist and the rationalist, are soon encountered. The case presented by the rationalist group of authorities may be thus summarized; deflection is the result either of carelessness or of differences in the dates of building the nave and the chancel respectively. We will consider first the explanation involved in the question of dates. It is generally believed that the choir of a church was often consecrated as soon as it was completed, the consecration of the nave or vestibule being held over until that part of the building was, in turn, ready for use. For instance, as Mr Parker pointed out, the Norman choir and transepts of the earlier Westminster Abbey are known to have been consecrated in A.D. 1065, but the nave, if one were ever added, was probably not finished until the twelfth century. Separate alinements may, in such cases, have been set out, and slight errors have been made during the operation. Again, in some of the churches which show inharmonious alinements, the nave and the choir manifestly belong to different epochs, one or other portion having been rebuilt. The architect of the later period unconsciously took an orientation which deviated from the first axis, or, according to the alternative view, he was actually unable to make the axes correspond. If we assume that he employed a magnetic compass, there is a third possibility of error in the variation of that instrument. But all these hypothetical causes of miscalculation are removed if we attach weight to a simple suggestion which has been made by one or two writers. It is submitted that the axis of the nave or the choir, whichever portion was already standing, would probably be hidden from the mason’s view, through the temporary blocking up of the chancel arch. This might render harmonious alinement a task of some difficulty[576]. It has been averred that every case of deflection occurs in a church which has been partially rebuilt; hence the lack of agreement. It is difficult to say whether this statement is absolutely correct, but it seems to be true in many instances. Even so, why are the misalinements practically confined to re-buildings of the thirteenth and fourteenth centuries?