WordWeb Online

1. (used to introduce a logical conclusion) from that fact or reason or as a result
   "therefore X must be true"
   - hence, thence, thus, so
    
2. As a consequence
   "he had good reason to be grateful for the opportunities which they had made available to him and which therefore led to the good position he now held"
   - consequently

1. And for this reason
   "You are too nice, and therefore tend to be exploited"
   - so

Encyclopedia: Therefore