Geometric ornament in Great Seljuk architecture has been the subject of diverse and sometimes conflicting interpretations in Islamic art scholarship. This diversity raises a methodological question concerning how such interpretations are constructed and validated: on what grounds have scholars developed different historical, symbolic, or metaphysical explanations from the available works and evidence, and how have they justified their validity? Situated within the historiography of Islamic art, this study critically examines and compares the logics of reasoning, interpretation, and validation in three major approaches to Seljuk geometric ornament: descriptive-archaeological, traditionalist, and historical-contextual. Rather than interpreting the ornament itself or privileging one existing reading, the study reconstructs how selected works transform data into evidence, connect evidence to claims, and establish the validity of their conclusions. The analysis shows that the descriptive-archaeological approach provides a strong empirical basis for documentation, dating, and stylistic classification, but requires additional mediating evidence when advancing broader explanatory claims. The traditionalist approach foregrounds the symbolic and metaphysical dimensions of geometry, while its interpretations of particular historical works largely depend on the internal coherence of its symbolic system and accepted correspondences unless independently supported by historical evidence. Historical-contextual approaches are themselves heterogeneous, comprising cultural-perceptual, semiotic-contextual, symbolic-ideological, and technical-workshop models, each facing distinct problems in moving from formal or historical indications to explanation. The study concludes that interpretive validity depends not on methodological affiliation or internal coherence alone, but on the relationship between research questions, data, evidence construction, reasoning, the scope of claims, and the limits of generalization.