Thomas Hobbes belived that political philosphy begins with the study of human nature. He thought that there are 2 keys to understanding human nature ie. self knowledge, whereby through honest intospection, one can gain an indication of the nature of humans thoughts; hopes and fears. The second key is through knowledge of the general principles of physics. He was a materialist and believed that in order to understand human nature, we must first understand 'body' or 'matter' of which we are entirely composed. He adopted Gallileo's principles of the conservation of motion and used theses principles to establish his materialst mechanic view of human beings. His conception of human nature entails that all people are rational and equal. All people have roughly the same level of skills and strength, and so therefore any human has the capacity to kill any other. His view is that all people possess roughly the same physical and mental abilitites and are therefore equally able to get what we want.
In terms of rationality, Hobbes thought that humans can distinguish between pleasure and pain (ie. good and evil) and so therefore, as rational agents, we seek pleasure and avoid pain. Hobbes speaks of The State of Nature and this basically means to imagine what life would be like without a government. He arrives at the reasonable assumption that in The State of Nature there is a scarcity of goods: If 2 people desire the same kind of thing, they will therefore desire to possess the same thing, leading to conflictual situations. Hobbes thought that equality, scarcity and uncertainty were the 3 main principle causes of quarrel. Hobbes thought that life in The State of Nature would therefore be a state of war. This view was that any reasonable person can escape The State of Nature if they applied certain principles which he called The Laws of Nature.
The Laws of Nature are precepts of reason, which, if followed, would result in peace. The Laws of Nature say that you should seek peace wherever possible, but if you cannot achieve peace, you should defend yourself at your disposal; You should give up the right to defend yoursef to the extent that is neccessary to achieve peace, provided other's accept the same limitations; You shouls keep you promises (covenants), and; You should not let those who keep their promises, regret doing so.
Hobbes's Laws of Nature stem from rationality. He says that reason dictates our passions, which drive our actions, therefore we seek pleasure and avoid pain. The State of Nature is so 'painfull' that our reason leads us to want to escape it. We therefore imagine a set of rules, which, if everone obeyed, would preserve our lives.
Hobbes however, doubted whether humans would ever apply The Laws of Nature, unless these laws (and other laws) could be enforced. Hobbes therefore sees it as essential to establish a state with someone having a monopoly of ultimate authority. His Social Contract assesses how we would behave in the abscence of certain influences. In order to escape The Sate of Nature, we need to find a way to compel others to follow The Laws of Nature, all of the time. In order to attain this guarantee, everyone transfers their rights into the hands of one person or assembly, and in return, you gain certain civil freedoms and the certainty that other's will respect your rights, because if they do not, they will be punished by the sovereign. You therefore trade in fear of other's; in a fear of the sovereign punishing you, if you disobey.
For Hobbes, a 'common power' was neccessary to make sure that we keep The Laws of Nature, and benefit from it, as our reason says we will. The sovereign comes about in one of two ways: Institution or Acquisition. The former is when there is an agreement between all the people, the majority must consent to the specific sovereign chosen, and the rest must consent or be destroyed, as at this point, the covenant becomes binding. The covenant is amongst the citizens, and not between the citizens and the sovereign, therefore Hobbes holds that the sovereign has no obligation to the citizens. The latter manner in which the sovereign may be established is through common wealth by acquisition, and this is when the people submit to a sovereign that has conquered them. In both cases, the sovereign is neccessary to remove the fear and danger of violent death, as Hobbes thinks The Sate of Nature is "solitary; poor; nasty; brutish and short" He thus feels that we will live in constant fear and danger of violent death, and therefore we need the sovereign to protect us. He says that the sovereign will protect us from the dangers of The State of Nature, only if it has absolute power. Hobbes also believed that outside a state, no moral consideration apply. He believed that morality is made possible by the state.