Throughout most of the eighteenth-century, it was common for drafters to begin every noun with a capital letter, just as Germans do today. This convention was fading by the time the Constitution was drafted (1787), but Gouverneur Morris, who actually penned the final document, elected to follow it. That is why nouns in the original Constitution are capitalized.
However, Morris made a few mistakes, and some nouns were left without capitals. They include: “defence” in the Preamble, “credit” in Article I, Section 8, Clause 2 (the congressional borrowing power); “duty” in Article I, Section 9, Clause 1; and “present” in Article I, Section 9, Clause 8.
Two years later, when (under the guidance of James Madison) the First Congress drafted the Bill of Rights, it elected to drop the capitalization rule. Nevertheless, a few mistakes crept in: Several of the nouns in the Bill of Rights were capitalized.
The capitalization or non-capitalization of a word has no substantive effect, although when used to introduce a phrase it can serve as a clue to meaning.
cross-posted from the Electric City Weblog