The US has one of the purest systems of separation of powers, as well as one of the strongest systems of checks and balances. This is where each arm monitors the operations of the arms. I will discuss this in terms of the American Washington system. Westminster systems need not apply.

Back before liberal democracy they had a problem where kings, despots, tyrants etc used to make laws up on the spot, enforce those laws on the spot, hand down sentences on the spot and tax people on the spot. It represents arbitrary government and got a bit of a bad name.

The American founding fathers looked to all the present systems of government, looked to the enlightenment philosophers and decided to come up with something better - that was resilient to the negative and selfish passions of politicians. One that would make America free forever from the tyranny and despotism of being subject to a King.

They put down all this thinking into the US Constitution and Hamilton, Madison and Jay explained it in great detail in the Federalist Papers. A must read for anyone interested in the philosophical basis of the American republic.

• Executive: In the US system this is the Administration headed by the elected President. The executive cannot make laws, nor interpret them or pass sentence on them. The President can only execute the laws that the legislative branch of government has made.

• Legislative: This can be bicameral or unicameral. In the US it is bicameral with a Senate and a House of Representatives. These two houses make the laws and money bills. These are the laws that the Executive must execute. It also provides the funding to execute those laws.

• Judicial: This branch interprets laws that are made by the legislative.

The separation of powers doctrine also contains counterbalance. For instance the legislative must approve the executive's appointments to the judicial. The executive can veto a legislative bill. The judicial can determine a law made by the legislative unconstitutional.

These stop the branches acting in a tyrannical manner in their own little fiefdoms of distinct power.

This is all tied together with a constitution. A single document that describes in detail the powers of each branches and the checks and balances on each branch. The constitution defines the limits of executive, legislative and judicial authority. As a consequence, when interpreting government action, it is an absolute.

Through the factional system, politicians have impugned themselves to varying degrees from the limits written into constitutions. The next iteration or innovation for liberal democracy will probably be having a democratically elected magistrate who's sole concern and authority, is to ensure that the constitution is not being broken and tyranny being committed.