Generating reasons for arguments quickly normally arises from experience and deep knowledge. But we are ultimately limited in what we can experience and know. Having an understanding of how to generate arguments with topos, called commonplaces, allows a rhetorician to generate reasonable positions from a finite amount of resources. 

Dating back to the ancient Greeks, the topoi (pl. topos), allowed rhetoricians to find persuasive arguments quickly. In my experience, or rather, my student's experiences, the topoi are best suited for deliberative arguments. Arguments about definition and truth are not as compatible, but still primarily lean on a philosophical, historical, and literary sources to generate positions.