Article in Dative = "by" in Romans 5:15?

Bill Ross (wross@farmerstel.com)
Wed, 3 Jun 1998 15:00:09 -0500

Romans 5:15:

EI GAR TW TOU ENOS PARAPTWMATI

is translated

"For if through the offence"

Question: Why is "TW" translated "by"?