Up to now, two analytical categories have been used in modern political science to study and identify organised political forces, i.g. political parties and pressure groups. Nevertheless, it is obvious that political analysts feel that these two categories are not sufficiently comprehensive to cover the wide range of groups that exists. I do not intend at the present moment to discuss at length the theories that have been developed by students of politics with regard to parties and pressure groups.
We shall confine our remarks to stating that the criterion for distinguishing one group from the other is that whilst parties attempt to conquer power in order to exercice it directly, pressure groups, on the contrary, limit themselves to bringing pressure to bear on political authorities whilst remaining outside these authorities. Secondly, it can also be said that whilst on one hand political parties have an overall view of the community, pressure groups, on the other hand have a partial or sectional view of this community. On the third place-some authors add-whilst political parties combine heterogeneous groups that give a heterogeneous social infrastructure to them, pressure groups, on the contrary, are the representation of homogeneous interest (1).
Even a cursory examination of political life in the western world leads us, nevertheless, to the conclusion that such a classification should be treated with extreme care. This is because, on one hand, political forces are constantly evolving, so that it would be preferable to talka bout a sort of « continuum » which possesses « ideal poles », rather than a series of groups which are separate and distinct from each other : the different organised political groups could be placed, according to circunstances, between these poles but each one of these groups could vary its own position in the continuum during its lifetime thus, the case of a group that starts its life as an interest group but later tends to develop towards the « party pole » (2). On the other hand, it can be seen that it is difficult to situate certain organised political groups in the context of political parties and pressure groups : this is the case with paramilitary organisations, « conspiratorial groups », or that of the groups which G. Sartori has called « struggle groups », or that of the groups which I have called « political clubs ».