Actually, many jurisdictions still use E, but the consensus seems to be that those who don’t chose F as a failing grade instead of E because F can easily be understood as fail, and E could too easily be mistaken for excellent.
The most common answer will likely find to this question is that E was removed from the letter grading system because E could be too easily mistaken to mean excellent. To me, this doesn’t pass the smell test. Couldn’t A mean awful, B mean bad, C mean crap, and D mean dunce?
Another explanation is that F is easily understood to mean fail and it can reasonably be applied to all failing grades. This does make some sense because if both E and F constituted a failing grade, then what is the point of differentiating them since the outcome is the same.
There’s also a bit of a flaw in the question because, in fact, many letter-based grading systems actually do include an E grade. It’s true that most grading systems in the US and Canada don’t give out E grades but even here some do and in some places, a failing grade is an E and there is no F.
From a historical perspective, the letter-based grading system can be traced back to Mount Holyoke College in Massachusetts in 1897 where they began giving letter grades from A (95-100%) through E (failed, below 75%). Shortly thereafter they bumped E up a little and represented a fail (below 75%) with the letter F.
It seems that in the 1930’s most schools in the US had removed the E grade, however, after World War 2, some reverted to E from F.
The E is actually used in some grading systems, though. Since WWII, some schools, mostly Midwestern, have used E instead of F to denote a failing grade. A few schools even use U (“unsatisfactory”) or N (“no credit”) instead of F.
What grades match each letter now?
There is a much wider variation in how letter grades are applied that you might expect. In Ontario, CA where I grew up, the grades are A (80-100%), B (70-80%), C (60-70%), D (50-60%) and F (< 50%). Other provinces in Canada are a little different.
According to Wikipedia, the American grading system is A (90-100%), B (80-90%), C (70-80%), D (60-70%), and E or F (< 60%) but that seems to vary by location as well.
Regardless of the system you follow, you would do well to try to avoid an E or F, unless they mean Excellent and Fantastic.