Identifying a form of government is also difficult because many political systems originate as socio-economic movements and are then carried into governments by parties naming themselves after those movements; all with competing political-ideologies. Experience with those movements in power, and the strong ties they may have to particular forms of government, can cause them to be considered as forms of government in themselves.
One method of classifying governments is through which people have the authority to rule. This can either be one person (an autocracy, such as monarchy), a select group of people (an aristocracy), or the people as a whole (a democracy, such as a republic).
The difference of Commonwealths consisteth in the difference of the sovereign, or the person representative of all and every one of the multitude. And because the sovereignty is either in one man, or in an assembly of more than one; and into that assembly either every man hath right to enter, or not every one, but certain men distinguished from the rest; it is manifest there can be but three kinds of Commonwealth. For the representative must needs be one man, or more; and if more, then it is the assembly of all, or but of a part. When the representative is one man, then is the Commonwealth a monarchy; when an assembly of all that will come together, then it is a democracy, or popular Commonwealth; when an assembly of a part only, then it is called an aristocracy. Other kind of Commonwealth there can be none: for either one, or more, or all, must have the sovereign power (which I have shown to be indivisible) entire.
Certain major characteristics are defining of certain types; others are historically associated with certain types of government.