if activity is commercial then it does not matter whether the particular instance of the activity directly affects interstate commerce, as long as the insance is party of a general class of activities that, collectively, substantially affect interstate commerce. if the activity is NOT commecial, then there must be a pretty obvious connection between the activity and interstate commerce (the link between possession of a gun in a school zone and interstate commerce is too tenuous to qualify as substantial effect because if it did there would be essentially no limit to Congress' Commerce power - US v. Lopez) less deference to Congress to the fact that congress believed that the activity has the reqiste substantial effect; not enough that Congress had a rational basis for believing that the requisite effect existed