This paper analyzes the construction λανθάνω + participle, which is one of the most interesting uses of the participle in Ancient Greek. In such a construction - and in few others - the participle is usually translated according to the grammatical categories codified by the finite verb, whereas the finite verb is translated by an adverbial element which only expresses its semantic content, e.g. "unawares" in the case of λανθάνω. This article connects this characteristic to the logical-semantic property of symmetry with regard to "inversed" occurrence, namely the case of a finite verb plus λανθάνω in participle form, where the participle is usually cosubordinate (or in some cases a predicate modifier), is characterized by conceptual closeness to the main predication, and conveys new information. It can be assumed that the symmetric construction of λανθάνω + participle arises from the apposition of a conjunct participle to the subject of an active form of λανθάνω. Symmetry implies the same semantic-pragmatic features of the inversed syntactic structure. This is likely to be the reason for its particular translation, in contexts where the participle conveys given information within the same information unit as the finite form of λανθάνω.