The "motivation domain" of an Enterprise Architecture addresses objectives in a broad scope ranging from high-level statements expressing the goals of an enterprise to declarations of requirements on business processes, services and systems. An important development regarding the incorporation of the motivation domain in a comprehensive Enterprise Architecture modeling language is the upcoming Motivational Extension to ArchiMate (based on the ARMOR language). The extension proposes the inclusion of concepts such as concerns, assessments, goals, principles and requirements to ArchiMate. We believe that careful definition of the semantics of these concepts is required, especially when considering that the motivation domain addresses subjective aspects of the enterprise. To address that, this paper focuses on an ontology-based semantics for the Motivation Extension. We interpret the concepts by using the Unified Foundational Ontology (UFO) as a semantic domain, and, as a result, propose well-founded recommendations for improvements of the extension.