It’s usually very hard to know whether something is in the Shahnameh because Ferdowsi has decided to give it emphasis, for whatever ideological or aesthetic purpose, or because he is simply reproducing his sources. However there are a number of pivotal moments in the poem for which we can be virtually certain that he had available to him sources that contradicted one another, and that he has chosen one version of a narrative over other versions. We see this in his treatment of the relations between the house of Sistan and the central Persian monarchy, in the way he handles the transition from pre-Zoroastrian Iran to Zoroastrian Iran, and in his presentation of Alexander, to name only the most spectacular examples. In each of these cases, and elsewhere in the poem, we can see that in dealing with any given narrative he chooses the version that emphasizes continuity rather than disruption, and a willingly accepted central authority rather than local irredentism. We can therefore posit an implicit ideology of continuous central authority, and relatively seamless transition through what otherwise might appear to be crucially disruptive events (e.g. changes of religion or dynasty). Since this ideology operates at cruxes where (because of our awareness of the existence of alternative and implicitly more disruptive versions) it momentarily becomes visible to us, we may be safe in assuming that it probably operates passim, throughout the poem, and at points where alternative versions have not come down to us.