Textually narrating the observed evidences relevant to the reasons why a video clip is being retrieved for an event is still a highly challenging problem. This paper explores the use of a commonsense ontology, namely ConceptNet, in generating short descriptions for recounting the audio–visual evidences. The ontology is exploited as a knowledge engine to provide event–relevant common sense, which is expressed in terms of concepts and their relationships, for semantics understanding, context-based concept screening and sentence synthesis. A principal way of exploiting the ontology, from extracting the event–relevant semantic network to the formation of syntactic parse trees, is outlined and discussed. Experimental results on two benchmark datasets (TRECVID MED and MediaEval) show the effectiveness of our approach. The findings show insights on the usability of common sense for multimedia search, including the feasibility of inferring relevant concepts for event detection, as well as the quality of textual sentences in meeting human expectation.