Of course I knew what she meant: she meant “the latter part of his career,” when in fact Chaucer did write The Canterbury Tales, or as much as he managed to finish before his death. Pretty clearly, she knows the meaning of “latter”; she just doesn’t know it’s a word.
This kind of problem is not limited to student writers. All of us mis-hear words and phrases: when the mis-hearing makes a new kind of sense we can call it a mondegreen, if we’re so inclined.
Sometimes we’re mis-hearing words we actually know, but confuse because of sound. I certainly know the words “bad,” “moon,” and “rise,” but when Creedence Clearwater Revival sang it, I (and evidently a lot of other people, if Google is to be believed) heard “There’s a bathroom on the right” instead of “There’s a bad moon on the rise.” For years I wondered why someone would put directions to a lavatory into a popular song….
Sometimes the confusion arises because we hear a word that is not familiar, but it sounds sufficiently like one we know that we assume it’s the one intended: “We know he’s Jewish because his grandson had a brisk,” for example. And we blithely go on to use the word we think we heard. As long as we’re just speaking, we might get away with it; but when we have to commit it to paper, we reveal our confusion to others, if not to ourselves.
And that’s all that happened here.
For me, of course, the sentence suggests Chaucer climbing to the heights of literary celebrity or achievement. But such a “ladder” part of his career would have predated The Canterbury Tales. The Book of the Duchess was probably the first real rung, an elegy commissioned by John of Gaunt for his dead wife. And up he went, with Parlement of Foules, The Legend of Good Women, and Troilus and Criseyde, among other works. The ladder part. Top rung: The Canterbury Tales. If he had lived longer, he would have needed a taller ladder.