As Kasper, I too am not a native speaker, but I have issues with this explanation. As stated by jaihare, in "I know who he is", the phrase "who he is" is an indirect question, which acts as the object of "know". Hence, "who" is an interrogative pronoun. But in "I know him, who he is", "who" is a relative pronoun (which happens to look the same as the interrogative.)Lucus Eques wrote: "who he is" is a clause that you will agree sounds correct. For example, "Who he is astounds me!" "Who he is makes everyone tremble," etc. Therefore, "Who he is, I know him." Thus: "I know who he is." In reality, what has been omitted is the word "him" : "I know him who he is." So "him" is the missing object you're looking for, and its objectivity is transferred fully upon the clause "who he is," though it shows no accusative marker.
Explaining or defending a grammatical construction by supplying a word that was not in the original, and argue that it is implied, is quite frankly a rather naive way of reasoning, and regrettably prone to err. Let me give another example: it is (or at least was) widely argued, that a construction such as "he is taller than I" is grammatically superior to "he is taller than me", since, it is said, what we "really" have is an "am" that is implied or understood: "he is taller than I [am]". Now, as it happens, this exact construction, and accompanying prescriptive explanation, also exists in Swedish (being, as it is, a relatively closely related language). The prescriptive grammars advocate, on the same reasoning as the English prescrivists, that it should be "han är längre än jag" (being word for word identical in structure to "he is taller than I"), but people tend to say "han är längre än mig", with "mig" = "me" in the objective case. Now, one difference between English and Swedish, and the reason why I started to discuss another language, is that Swedish has reflexive pronouns (which work fairly similarly to those in Latin). The exciting and interesting fact is that virtually everyone would say or at least accept "han är längre än sin bror" (="he is taller than his [own] brother"), while at the same time *"han är längre än sin bror är", with "är" (="is") added, is grammatically impossible! It must be "han är längre än hans bror är" (="he is taller than his brother is"). This demonstrates that, in Swedish at least, the argument that there is a word that is "implied" or "understood" is faulty.
Do you argue that "they saw him who was foretold" and "they saw who was foretold" is (or was) semantically equivalent?Lucus Eques wrote:Have you read the King James English version of the Bible? In it you'll read many unmodern forms of English, that still fully qualify as Modern English and are officially part of this very language (including "thou" and "thy," inter alia). Constructions such as, "They saw him who was fortold," and so forth, are much more common. Though the hodiern English eschews these redundancies, they used to be quite normal.