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"We know of no rule for construing the extent of such powers, other than is given by the language of the instrument which confers them, taken in connexion with the purposes for which they were conferred."
The words are, "Congress shall have power to regulate commerce with foreign nations, and among the several States, and with the Indian tribes."
The subject to be regulated is commerce; and our constitution being, as was aptly said at the bar, one of enumeration, and not of definition, to ascertain the extent of the power, it becomes necessary to settle the meaning of the word. The counsel for the appellee would limit it to traffic, to buying and selling, or the interchange of commodities, and do not admit that it comprehends navigation. This would restrict a general term, applicable to many objects, to one of its significations. Commerce, undoubtedly, is traffic, but it is something more: it is intercourse. It describes the commercial intercourse between nations, and parts of nations, in all its branches, and is regulated by prescribing rules for carrying on that intercourse. The mind can scarcely conceive a system for regulating commerce between nations, which shall exclude all laws concerning navigation, which shall be silent on the admission of the vessels of the one nation into the ports of the other, and be confined to prescribing rules for the conduct of individuals, in the actual employment of buying and selling, or of barter."
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Hence, "The nature of any particular transaction is irrelevant. The nature of the market is what determines applicability."
"He was talking about states impeding interstate commerce for their own benefits."
Means the same as, " the intent there was to remove State power to favor their own players over those of another State."
Basically, interstate (and foreign) commerce is any commerce which, for a particular state, would be properly described as foreign commerce if that state were an independent country.
How is the state involved if I sell a hotdog at a carnival to someone? When the hotdog was sold from a meat plant out of state to the market where I bought it then there was interstate commerce. The sale at the carnival was not. And the state had no means to favor one other state over another in the second transaction.
Also, how is the 15 year old AR in my closet involved in interstate commerce once is was sold to the end user? Sorry, I view the use of the commerce clause as a thin excuse for a naked power grab by the fedgov. You seem to favor it, but it is a prime reason that the fedgov wields more power than they were ever intended to have.