In this paper an attempt is made to examine the meaning of analogia in Saint Thomas by comparing it 'with the sense given it by Cajetan. So far most studies of Saint Thomas' doctrine of analogy have been biased by Cajetanain interpretations of it, and have been, for the most part, made from the viewpoint of metaphysics. Although the concept of analogy in Saint Thomas has a key function in his metaphysics, yet he is concerned with it from the logical point of view. In other words, he considers analogy as " media inter aequivocationem et univocationem." On the other hand, since Saint Thomas made use of analogy to establish metaphysics as he really meant it, we should not say that it is enough to determine his logical sense of analogy. Rather, we have to clarify the logical characteristics of his concept of analogy in order to understand his metaphysics in the full sense. An analyis of Saint Thomas' concept of analogy from the logical viewpoint, shows that it means " ratio partim diversa, et partim non diversa." Since Cajetan did not fully analyze it from the logical viewpoint, he misunderstood it, and accordingly, could not fully grasp Saint Thomas' metaphysics. Cajetan seems to have misunderstood his master's concept of analogy by mistaking the three species of .analogy -analogia secundum esse, analogia secundum intentionem, anallogia secundum esse et intentionem - for Saint Thomas' true doctrine of analogy. 橋本孝先生古希記念論文集