The following definitions are given to clear up words that are often mangled by political candidates that wish to re-define their opponents.
Conservatism:
Synopsis: Conservatism is the tendency to prefer existing situations and support traditional power structures rather than change.
Conservatism received its classic formulation in the works of the British statesman Edmund Burke, notably his Reflections on the Revolution in France (1790), in which he rejected the principles of the French Revolution and presented a comprehensive philosophy of society and politics. Burke viewed society as an organic whole, with individuals performing various roles and functions. In this society a natural elite—by virtue of birth, wealth, and education—is supposed to provide the leadership. The community is held together by venerable customs and traditions; gradual changes can be made, but only when they have gained wide acceptance. – From MSN Encarta
Liberalism:
Synopsis: Liberalism is the tendency to prefer the modification of existing situations and power structures in order to improve individual rights for all.
An influential early liberal was the English philosopher John Locke. In his political writings, which deeply influenced the framers of the U.S. Constitution, he argued for popular sovereignty, the right of rebellion against oppression, and toleration of religious minorities. According to the thought of Locke and his many followers, the state exists not to promote people’s spiritual salvation, but to serve its citizens and to guarantee their life, liberty, and property under a constitution. – From MSN Encarta
Radicalism is avocation of the views, practices, and policies of extreme change. The bill of rights is an example of a radical change. This bill was ratified in 1791, three years after the Constitution.
The word was first used in the political sense in England, when the British statesman Charles James Fox asked for “a radical reform” that would extend the franchise to universal manhood suffrage. The term radical afterward indicated those in support of parliamentary reform. After the passage of the Reform Bill of 1832, a measure primarily benefiting the middle class,[…] – From MSN Encarta
Reactionary:
Synopsis: Resistance or opposition to a force, influence, or movement frequently with a tendency toward a former and usually outmoded political or social order or policy.
Reactionary comes from the French word réactionnaire, coined in the early 19th century. It was the first of the two words coined (the other being conservative, from the French word conservateur) for the opposition to the French Revolution. “In parliamentary usage, the monarchists were commonly referred to as the Right, although they were often called Reactionaries.” This is the first time the word was used to mean “A movement towards the reversal of an existing tendency or state” or a “return to a previous condition of affairs.”
The earliest English-language use cited in the OED is by John Stuart Mill in 1840: “The philosophers of the reactionary school—of the school to which Coleridge belongs.” – Wikipedia.org