Question

1. This is the boy whom I spoke of yesterday.
2. This is the boy of whom I spoke of yesterday.
3. This is the boy who I spoke of yesterday.
4. This is the boy of who I spoke of yesterday.
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All are correct except #4? Am I right? Why do we use 'who' in #3? Traditionally we used 'whom.' When did people start to use 'who' in this sentence?

Answer 1

who is still incorrect in #3 and #4. In #2, you do not need the second "of". "of whom" is clear without it. Without the second "of", #2 actually is better than #1 (it's reads better and sounds better), but neither is incorrect.