Most of my schooling was scored with letter grades, so I’ve always thought in those terms. (4.0? What is that, A+?) But in my experience, letter grades were squishy and imprecise.
In grade school our teachers marked A,B,C, D, F. Then they decided to add a new mark, “I” for “Improving.” The rationale: if a student’s work was failing but the student was trying harder, “I” was an encouragement; still not passing, but better than F. Soon, students whose work had been D and were slip-sliding down that awful slope were given an I grade to warn them they had started to fail. (“How’s Henry doing in Math? “Sorry, I’m afraid he’s improving.”)
Meanwhile Juilliard, that most competitive of music schools, was also marking A,B,C,D,F. However some students came along who were obviously better than those getting A’s, so teachers invented a new top grade: G for good. A few years later the pianist Van Cliburn arrived and was a better student in every way. His teachers gave him E (excellent), thus: E,G,A,B,C,D,F.
Letter grades: not intuitively obvious.