Article 2, Section 2, Clauses 2 and 3
Thomas Jefferson to Wilson Cary Nicholas7 Sept. 1803Works 10:10
I am aware of the force of the observations you make on the power given by the Constn to Congress, to admit new States into the Union, without restraining the subject to the territory then constituting the U S. But when I consider that the limits of the U S are precisely fixed by the treaty of 1783, that the Constitution expressly declares itself to be made for the U S, I cannot help believing the intention was to permit Congress to admit into the Union new States, which should be formed out of the territory for which, & under whose authority alone, they were then acting. I do not believe it was meant that they might receive England, Ireland, Holland, &c. into it, which would be the case on your construction. When an instrument admits two constructions, the one safe, the other dangerous, the one precise, the other indefinite, I prefer that which is safe & precise. I had rather ask an enlargement of power from the nation, where it is found necessary, than to assume it by a construction which would make our powers boundless.
The Founders' Constitution
Volume 4, Article 2, Section 2, Clauses 2 and 3, Document 27
The University of Chicago Press
The Works of Thomas Jefferson. Collected and edited by Paul Leicester Ford. Federal Edition. 12 vols. New York and London: G. P. Putnam's Sons, 1904--5.
Easy to print version.