After returning to Montpelier, without a chosen career, Madison served as a tutor to his younger siblings. Madison began to study law books on his own in 1773. Madison asked a Princeton friend William Bradford, a law apprentice under Edward Shippen in Philadelphia, to send him an ordered written plan on reading law books. At the age of 22, there was no evidence that Madison, himself, made any effort to apprentice under any lawyer in Virginia. Frustrated by the failure of the states to supply needed requisitions, Madison proposed to amend the Articles of Confederation to grant Congress the power to independently raise revenue through tariffs on foreign imports. During his first stint in Congress in the 1780s, Madison came to favor amending the Articles of Confederation to provide for a stronger central government. According to Chernow, Madison's support of the Virginia and Kentucky Resolutions in the 1790s 'was a breathtaking evolution for a man who had pleaded at the Constitutional Convention that the federal government should possess a veto over state laws.'