By using intuition or improvising. The term comes from World War II, when aviators used it to describe flying when instruments did not work or visibility was poor. After the war it quickly came into more general use, as in “Use a score? No, I just conducted the overture by the seat of my pants.”

Using experience, guesswork, or instinct rather than some calculated or scientific method. The term originated among World War II aviators, who so described flying when instruments were not working and/or weather interfered with visibility. It was transferred to other activities in subsequent decades. M. Walker used it in The National Front (1977): “Mussolini had governed by the seat of his pants.”