Government as a necessary evil
From the outset, Paine makes it clear that he is not particularly fond of government, whose sole value he thinks lies in "restraining our vices". For Paine, the natural state of man is to live without government, and government's existence is justified only to the extent that it alleviates problems that would be created by this natural, anarchic way of life. If a government fails to improve society or, worse, actively causes some of the same troubles that would result from anarchy, it is particularly blameworthy.
State of Nature
Much of Paine's analysis proceeds by considering an imagined natural state in which man might have first found himself. This method of analysis, popularly used by political theorists such as Locke and Hobbes, considers man as he might have been before society was formed. Such an analysis then imagines what man would have been like, and what rights he might have had, if it were not for the interference of outside circumstance. Paine uses this imagined natural state to analyze a political dilemma with his parable of the settlers first coming to America. Furthermore, in discussing monarchy, Paine presumes men to be "originally equals", and in doing so, hearkens back to some imagined age where he presumes men to have all been equal.
The Inevitability of American Independence
A linchpin in Paine's argument is that America will eventually be independent. At times, he presents this as a simple fact that everyone accepts, but occasionally, he argues for it, citing the extent of the rift separating the colonies and the English king. Since many people were uncertain about the idea of a revolution that would sever them from the king, establishing the principle of American independence was an important first step for Paine to take in his arguments. By convincing his audience that America will be independent some day, it is much easier for Paine to make the case for an immediate and full rebellion.
The Inevitability of British Oppression
Yet another key point in Paine's argument derives from considering what will happen if America reconciles with Britain. Paine argues that even if the colonists reach an agreement with Britain, the problems that have developed between the colonies and the king will inevitably repeat themselves. New taxes will be levied and parliament will interfere with colonial life. Paine attempts to demonstrate this in two ways. First, he points to the history of colonial relations with Britain, especially the events surrounding the Stamp Act. Second, he attacks the structure of Britain's government, arguing that it is corrupt and unjust, and will inevitably lead the British to continue mistreating the colonies.
America's relationship with the rest of Europe
Paine is acutely aware of the benefits to be reaped through developing strong relationships with European countries other than Britain. This informs his argument in a number of ways. First, Paine points out that it would be advantageous for America to form commercial and political ties with these nations. Second, he notes that the current political arrangement of America's being subservient to Britain precludes the colonies from being able to independently engage in such alliances. He concludes that only if the colonies declare independence, will they be able to reap the opportunities offered by alliance with various European nations.
The Problems with Monarchy
A large part of Common Sense is dedicated to attacking monarchy, both as an institution and in its particular manifestation in Britain. Paine puts the theoretical attack in Biblical terms, arguing from the text of the Bible that the monarchy originated in sin. Paine presents his specific problems with the British monarchy, with his attack on hereditary succession and with the numerous grievances he makes against the present king.