Every individual has the right to pursue knowledge, to engage in research, or to teach independently of any political control. Academic freedom is desirable because knowledge is best discovered by the open investigation of facts and opinions. Nations exercise control over academic and educational systems. Some exploit this control for the purpose of indoctrination. Political theorists as diverse as Plato and Marx have argued that education gives people power to change their lives and enables whole societies to develop. The value of education can be illustrated by its impact in poorer countries. For the individual, education means access to better-paid, more varied jobs and higher status. Governments usually wish to hold down the potentially limitless costs of education while ensuring the production of a skilled and law-abiding citizenry, whereas others may have concerns about curriculum, assessment and discipline. In consequence, battles may be fought, but are rarely conclusively won.