What is just a pronoun in this sentence. what = the thing that what used to seem to the great majority civilized = a thing that the majority of people believed was true That was what I thought. = That was the thing that I thought. You can also use the other question words in a similar way: how = the way that when = the time that where = the place that why = the reason that who = the person that

The answer to your question is: "What used to seem to" = "What once seemed to" = "What once appeared to". The length and complexity of this sentence's many clauses require too much patience from listeners. Whether or not it is grammatical hardly matters because people will not put in the necessary effort to understand it. To simplify analysis of this sentence, let us make these substitutions: X = "the right of society to retribution is this world with prospect of life in another" Y= "to the great majority of civilized humanity" (a parenthetical thought that plays no essential role) Z= "the assurance of another life beyond the grave" W= "A feeling for THE value of human life has become deeper and more widespread." Since Y is a parentetical thought, it ought to be isolated by commas or omitted completely W is a complete sentence. As such, it needs to be connected to the previous sentence by a conjunction like "because", "hence", etc. Lacking such a conjunction it MUST be a new sentence. You are not allowed to separate two complete sentences with merely a comma. Now, making minor grammatical corrections, the sentence becomes: The only arguable plea for capital punishment is X, but since what used to seem [,Y,] (to be) Z, (the validity of that plea) has become less certain. [New Sentence] W.

This passeage is not super well written, so the meaning is difficult to understand. By saying "used to seem" they are saying that in the past the author believes that the majority of people believed in some sort of afterlife, and now that is in question. They are saying "seems to" because they do not have any actual evidence this statement is true. It is more the authors opinion.

It means 看似

The sentence could be written better to avoid any ambiguity. Or better still completely rewritten from scratch. ------------- ----- ,but since what used to be seen by the great majority of civilised humanity. As become an assurance of another life beyond the grave has come to be less certain, a feeling for --> continue here Actually when trying to make it better it became nearly impossible. 1 correction in the sentence or overall phrase just perpetuated another problem further down into the sentence/phrase. A REWRITE IS COMPULSORY MANDATORY