&gt; Edit 2: Intel also makes compilers, to which I own, but never use.<p>I see this more and more often on Reddit, from posters I assume are millennials, and I am interested in the psychology of this error. Why do you put a &quot;to&quot; before &quot;which&quot;? You would not say &quot;I own to an Intel compiler&quot;.<p>I never see people make this mistake with other pronouns, either: for instance, they will correct turn &quot;I saw pg yesterday&quot; into &quot;pg, whom I saw yesterday&quot;. What is it about &quot;which&quot; specifically that makes it hard for kids to use?