Washington, appointed a Cabinet consisting of five people:
1. Secretary of State Thomas Jefferson
2. Secretary of the Treasury Alexander Hamilton
3. Secretary of War Henry Knox
4. Attorney General Edmund Randolph
5. Postmaster General Samuel Osgood.
A further position of Postmaster General was added. Hamilton was the most powerful member of Washington's cabinet, which soon polarized between Hamilton and Thomas Jefferson.
The Department of State was originally called the Department of Foreign Affairs and was created by statute on July 27, 1789. The name change came into effect on September 15, 1789. The Secretary’s main function was to serve as the principal adviser to the President in the determination of foreign policy. Washington appointed Thomas Jefferson as the first State Secretary on September 26, 1789.
On September 2, 1789, Washington reestablished the United States Department of the Treasury headed by the Secretary of the Treasury. The Secretary served as the principal economic advisor to the President and was the President's principal advisor in policy-making on economic and government financial policy issues. Alexander Hamilton was appointed by Washington to serve as the first Treasury Secretary on September 11, 1789.
To manage the United States Army, Washington created the position of Secretary of War to head the United States Department of War. This office was a continuation of the Continental Secretary of War. The Secretary’s duties were the formulation of Indian policy, planning for and managing the national military, and oversaw the creation of a series of coastal fortifications. Henry Knox served as the Continental War Secretary before the ratification of the United States Constitution and Washington appointed Knox to continue under him as the first Secretary of War on September 12, 1789.
When Washington signed the Judiciary Act of 1789, he not only created the federal judiciary but also created the office of Attorney General. Unlike the other Cabinet officials, the Attorney General would not head an executive department. The Attorney General’s functions would be to prosecute on behalf of the United States and to serve as the chief legal officer of the government by giving his advice and opinion upon questions of law to the President. Washington would appoint his former aide-de-camp Edmund Randolph as the first Attorney General on September 26, 1789. Along with the Attorney General, the United States Marshals Service as well as the United States Attorneys were established.
The final Cabinet level position created by Washington was the Postmaster General. The Postmaster role went back to 1776, with the function to provide postal service for the United States. Washington signed the Postal Service Act on February 20, 1792, creating the United States Post Office Department. Washington appointed Samuel Osgood to the post on September 26, 1789 as the first Postmaster General.
None of this explains why Washington's Cabinet didn't meet until 1793. The internets don't seem to have an answer and I'm not where I can access by book collection. Do any of you know why this was?