Abstract: Evaluation of information retrieval systems is a fundamental topic in Library and Information Science. The aim of this paper is to connect the system-oriented and the user-oriented approaches to relevant philosophical schools. By reviewing the related literature, it was found that the evaluation of information retrieval systems is successful if it benefits from both system-oriented and user-oriented ap- proaches (composite). The system-oriented approach is rooted in Parmenides’ philosophy of stability (immovable) which Plato accepts and attributes to the world of forms; the user-oriented approach is rooted in Heraclitus’ flux philos- ophy (motion) which Plato defers and attributes to the tangible world. Thus, using Plato’s theory is a comprehen- sive approach for recognizing the concept of relevance. The theoretical and philosophical foundations determine the type of research methods and techniques. Therefore, Plato’s dialectical method is an appropriate composite method for evaluating information retrieval systems.

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