[kiryandil]

While inalienable and unalienable are today used interchangeably with inalienable more common, the terms have historically sometimes been distinguished.

Regarding current usage being interchangeable:

The unalienable rights that are mentioned in the Declaration of Independence could just as well have been inalienable, which means the same thing. Inalienable or unalienable refers to that which cannot be given away or taken away. However, the Founders used the word "unalienable" as defined by William Blackstone in his Commentaries on the Laws of England, 1:93, when he defined unalienable rights as: "Those rights, then, which God and nature have established, and therefore called natural rights, such as life and liberty, need not the aid of human laws to be more effectually invested in every man than they are; neither do they receive any additional strength when declared by the municipal laws to be inviolable. On the contrary, no human legislature has power to abridge or destroy them, unless the owner shall himself commit some act that amounts to a forfeiture."...in other words a person may do something to forfeit their unalienable rights...for instance the unalienable right to freedom which can be forfeited by the commission of a crime for which they may be punished by their loss of freedom. However, once they are freed after serving their punishment their right is restored.

[Verginius Rufus]

News to me. I was under the impression that "inalienable," the form Jefferson wrote, was the correct form, and that the other was essentially a typo. My Webster's dictionary (1960 ed.) lists "inalienable" but not "unalienable." The "in-" prefix is a negative, from Latin, so has the same meaning as "un-."

But I have never read Blackstone.