title: "to_tsquery" on tsvector yields different results when using "simple" and "english"?
body: <p>I've been enlisted to help on a project and I'm diving back into PostgreSQL after not working with it for several years. Lack of use aside, I've never run into using tsvector fields before and now find myself facing a bug based on them. I read the documentation on the field type and it's purpose, but I'm having a hard time digging up documentation on how 'simple' differs from 'english' as the first parameter to to_tsquery()</p>
  
  <p>Example</p>
  
  <pre><code>&gt; SELECT to_tsvector('mortgag') @@ to_tsquery('simple', 'mortgage')
  ?column? 
  ----------
   f
  (1 row)
  
  &gt; SELECT to_tsvector('mortgag') @@ to_tsquery('english', 'mortgage')
  ?column? 
  ----------
   t
  (1 row)
  </code></pre>
  
  <p>I would think they should both return true, but obviously the first does not - why?</p>