title: Why does the Penn Treebank POS tagset have a separate tag for the word 'to'?
body: <p>The <a href="http://www.comp.leeds.ac.uk/ccalas/tagsets/upenn.html" rel="noreferrer">Penn Treebank tagset</a> has a separate tag <code>TO</code> for the word 'to', irrespective of whether it's used in the preposition sense (such as <code>I went to school</code>) or the infinitive sense (such as <code>I want to eat</code>). What purpose does this serve from an overall NLP perspective? Just tagging the infinitival 'to' separately makes intuitive sense, but I don't see the logic behind combining an infinitive and a preposition in a single tag.</p>
  
  <p>Thanks, and apologies if this doesn't fit the stack overflow guidelines.</p>