These principles are used as groundwork for further investigation. It was not until the nineteenth century that the phenomena of the State came to be regarded as a proper field for scientific investigation and since then many methods and approaches have been suggested and employed.
Auguste Comte suggested three principal methods of investigation, viz., observation; experiment; and comparison. Bluntschli considered philosophical and historical as the only two methods, which need be used for investigation and correct conclusions.
John Stuart Mill recognised four methods: (1) the chemical or experimental; (2) the geometrical or abstract; (3) the physical or concrete deductive; and (4) the historical method. Mill held the first two methods false and placed emphasis on the deductive and the historical methods only.
James Bryce held that observational; experimental; historical; and comparative methods were the only correct and proper methods to give conclusive results. Deslandres, a French scholar, recognises six methods: the sociological; the comparative; the dogmatic; the juridical; the method of good sense; and the historical method.
Some recent writers have emphasised the importance of sociological, biological, psychological and statistical methods of investigation. Contemporary political scientists significantly recognise and practice the psychological method with close ties to Economics.
Great importance is also given to comparative and statistical methods, the latter especially in the study of public opinion. In United Kingdom seven different methods are in use: historical, juridical, philosophical, institutional, analytical, observational and sociological.
The sociological method endeavours to relate the political system of a country to the social structure, habits, ideas, psychology and customs of the community. Robson advocates the analytical method. The Marxist dialectical method is followed in Communist countries.
According to Schaff and Eurlich, the basic principles of Marxist dialectical method lies in postulating the examination of problems in their integrity, that is, in examining phenomena in their interdependence and mutual relations.
They observe that in order “to attain knowledge of political reality, the Marxist dialectical method makes use of sociology which is built on a consistent material basis, and resorts, in turn, to an analysis of the social process in terms of the property relations which exist in any given society.”
There is, therefore, no single method which can come to the rescue of a political scientist and help him to unfold the phenomena of the State and government with some degree of precision.
The generally accepted methods of political investigation are: (1) the Observational Method. (2) the Experimental Method, (3) the Historical Method, (4) the Comparative Method, (5) the Method of Analogy, and (6) the Philosophical Method. To these may be added the Statistical or Quantitative Method.