Up to now we have been describing the nature of the political system. Every political system has a definite form. Like every social system, it is a definite mode of behaviour, which can be actually observed. It consists of various units, called structures. A structure is a unit of behaviour or interaction which is regularly performed and is actually observable. For example a court, is a unit of interaction (or behaviour) between a judge, an advocate, witnesses and clients? Ordinarily a court is called an institution. But in system analysis it is called a structure. Here we are not interested in the legal rules which govern its working, but in the actual behaviour or interaction between its units which is regularly performed. It is an operational concept, and can be tested and verified by empirical or experimental methods.<\/p>