What are the 4 limitations on congress power to tax?

The powers of Congress are enumerated in several places in the Constitution. The most important listing of congressional powers appears in Article I, Section 8 (see left) which identifies in seventeen paragraphs many important powers of Congress. In this section, we consider how the enumerated power of Congress "to lay and collect taxes" has been interpreted.

Currently, as of february 2016, an american traveling in france would be by the exchange rate. the weakness of the euro and the strength of the us dollar means that items in france cost less to an american than they otherwise would. of course, if this trend reverses and the us dollar weakens and the euro strengthens, such as was happening in early 2008, an american traveling in france would have an adverse experience because items would cost relatively more.