Tracing

Tracing is a technique of plagiarism that consists of closely following the shape of another secondary source. (I am unsure of who coined the term but it came up in the recent Sokal / Fischer controversy.) You might use some of the same quotes for the same purposes, or summarize at too great a length, too closely. It is true that you are free to use a quote you found quoted already elsewhere, but there are some cautions here. You should indicate "qtd in" if you found the source in a third place and didn't go back to the original. You should be careful about reproducing 3rd party errors (misquoting a source the same way someone else did). You should not take over several 3rd-hand quotes in a row from another source, especially if these quotes are distinctive or uncommon, or seemingly unrelated to the topic.

For example, if I am writing about Juan Ramón Jiménez and quote Wittgenstein, Barthes, and Derrida in that order. I don't own those quotes: I am not Wittgenstein, Barthes, or Derrida. But it is distinctive to use those exact authors and quotes to explicate Jiménez's poetry. You have to say "qtd. in Mayhew" in that context.

I feel that a summary of other material should be either

(1) Much shorter. You are extracting the essence of that source, not repeating all of its findings one after another.

(2) Much longer. You are taking something short in the original text and exploring additional implications.

(3) Shorter and longer at the same time, like an accordion. You are sometimes compressing, sometimes expanding, on what the other source said.

If you write a paragraph summarizing another paragraph of about equal length, then you are probably doing something wrong: why not just quote the paragraph verbatim if you are neither compressing nor expanding?