ar'ro-gate tr.v. — -gat-ed, -gat-ing, -gates.
» to usurp,
» to appropriate, assume, or claim (to oneself) unduly or without justification.
Mid 16th century. — Shorter OED 5th Ed.
» In use:
[President George W.] Bush has arrogated the power to imprison men without charges and browbeat Congress into granting an unfettered authority to spy on Americans. ("Barack Obama for President," Editorial, New York Times, 23 Oct. 2008.
Abrogate means to abolish (a law or custom) by authoritative or formal action; annul, repeal. Henry VIII abrogated Welsh customary law. Whereas arrogate, means, to usurp. You should not arrogate to yourself all of the credit for today's victory. (Wikipedia's "List of commonly misused English words" — http://en.wikipedia.org; and Dictionary of Modern American Usage, Brian A. Garner. New York: Oxford U. Press, 1998.)
It takes willful arrogance to arrogate to oneself something that is properly not one's own [emphasis added]. Not surprisingly, both arrogance and arrogate derive from the same root, arrogat, the Latin stem of arrogare, to claim for oneself (Shorter OED 5th Ed.). — B.J.