For many years, I have noted, as have some of my colleagues, a strange use of "in," usually with "which." Generally, I can understand the causes of students' errors, but this one puzzles me. Examples are collected here.

from s95pr05:

\-\There are a couple {of issues} here [{in which} [if they are fully understood] could clear things up.]

There are many other fallacies in this essay which weaken it, but the argument in which the author makes is relevant and should be taken into very high consideration.

Although the author Kent Scheidegger of the essay "Habeas Corpus is Abused by Concivts" relays many good examples of the abuse of this procedure, but the fallacies in which the author commits weakens his essay and argument dramatically. [See also: incomplete subordination.]