Both these sub-disciplines of philosophy refer to social phenomena - social philosophy to a greater extent than philosophy of law. But what are we to understand by this? Social phenomena are composed of relations between humans through actions, communication, perceptions, expectations. One cannot imagine any form of human understanding or decision making which is not influenced at least partially by relationships with other humans. We understand natural phenomena, for instance, in a certain way because we have received certain opinions concerning them from other humans.

If one were to regard every socially influenced perception or fact as the subject of social philosophy then all philosophising would be social philosophy or have social philosophy as its foundation and everything would be the subject of its attention. Such a viewpoint is not rare and belongs to the field of theory of the so-called "Frankfurt School" (Adorno, Horkheimer, Habermas etc.).

As other independent disciplines of philosophy, for example, epistemology, ontology, aesthetics, philosophy of language etc. are already established we will have to narrow down the subject matter of social philosophy. The mere influence of the relationship between humans on a fact or concept is not sufficient in order to allow a social phenomenon to arise. The relationships between humans in communities must be set out and determined according to how they exist in political, economic, family, legal or other communities. Thus the subjects of social philosophy are: states, economics, institutions, associations, businesses, families, parliaments, courts etc. and the relation of individuals to these groups.

One can collect these different forms of community under the term "society" on condition that one retains a certain critical distance in relation to this term - a consideration that is seldom taken on board nowadays. As only actually existing human communities are able to communicate and interact, the term "society" enables simply the conceptual summary of structures of interaction. In speaking of both individuals in terms of actions and of communities, such as political parties or businesses, as consisting of individuals one could nevertheless still regard these as collective actions and decisions of individuals, while the term "society" presents simply a bare abstraction. Certain individuals and communities can be summarised according to certain criteria, for instance, a common structure of communication or a common history.

A substantial part of social philosophy consists of social ethics, an area which poses questions concerning that behaviour which can be ethically justified within social communities and between the individual and social communities. Thus social ethics is in this respect part of practical philosophy. Aside from social ethics there is a theoretical facet within social philosophy which analyses social phenomena in relationship to other aspects of theoretical philosophy, for instance, philosophy of action, epistemology or philosophy of language.

Another significant element of social philosophy is political philosophy, that is, philosophy which refers to political communities. What are political communities? These are associations which make the final decision in a certain area on behalf of their members with a good prospect of the decision being accepted by its members. Within political philosophy one can also differentiate between political ethics and political theory.

What does philosophy of law deal with? A first response is simple: with law. To be more precise, philosophy of law deals with so-called "positive" law, that is, with actually existing and thus valid constitutional norms, laws, regulations, statutes, court decisions, customary law etc.. Positive law as the subject of research permits a delimitation of the philosophy of law from other disciplines within philosophy, for instance from philosophy of nature, philosophy of language or aesthetics with their subjects of  investigation, namely, nature, language and art.

However positive law is not only the subject of philosophy of law, but also further non-philosophical disciplines, for instance substantive law, the history of law or legal sociology. For a closer definition of the philosophy of law's field of study one must further ask: How does the philosophy of law differ in its perspective on the positive legal from other non-philosophical disciplines? In order to answer this question, it is advisable to turns ones eye away from the object of investigation, i.e. law, and to turns it instead towards the research method and the goal of the investigation with which these other non-philosophical disciplines investigate positive law.

Inquiries into valid law interprets the substantive law of a certain legal system from the perspective of an internal user, that is, from the perspective of judges and civil servants. Thus it integrates theoretical analysis and empirical description. However the actual character of inquiries into valid law is that of a "normative science", its actual purpose: the practical organisation and application of valid law. Also most law academics in universities take this user perspective whether they write articles on civil, public or criminal law and commentaries for use in the legal practice. The user perspective is often given a legal-political amendment by law academics. That means suggestions are made as to how laws, regulations and statutes could be changed. If one asks for a normative, non-legal, immanent reason for this kind of legal/political suggestion then one goes beyond substantive law and arrives at philosophy of law or legal ethics.

Philosophy of law, legal sociology and history of law refer to valid law in a manner different from inquiries into valid law, i.e. not from an internal but from an external perspective. They frequently consider not simply one legal system as substantive law typically does, but different current, bygone and future legal systems. Legal sociology describes the interaction of law with other spheres of reality, in particular the relationship between law and society. History of law describes the development and organisation of law

Philosophy of law on the other hand does not limit itself to the mere description of law from an external perspective, but strives towards a philosophical account of law. What we are to understand by a philosophical account depends on our fundamental understanding of the function of philosophy. Without having a detailed discussion of this central question of the function of philosophy at this point, it can at least be stated that the philosophical view of a topic in relation to its unique investigation takes on the more comprehensive uniqueness result of an integrated perspective

This more comprehensive, philosophical view of law leads in the case of the philosophy of law to two significant sub-disciplines: legal ethics and legal theory

Legal ethics subjects law to a justification or critique which is legal-external normative. Or to put it another way: within philosophy of law the core question of legal ethics is that of the justice of positive law. It does not concern itself simply with a system’s internal coherency, as inquiries into valid law does, but with a measure of justice, which is not positive law. The implementation of legal-ethical considerations are found on the one hand - as previously noted - in the politics of law (in laws, statutes and regulations) and on the other hand in the teaching of legal procedure, that is, reflection on methods for the application of law in court and administrative decisions.

Legal theory analyses the fundamental structures of law, e.g. its system and institutions, the sources and use of its language, its acquisition of knowledge , its logic and its implicit theory of action. The more philosophical disciplines and their academic subject counterparts play a role, for example, political philosophy and political science, philosophy of language and linguistics, epistemology and psychology, logic and mathematics, theory of action and decision psychology. Legal theory also stands in relation to legal policy and legal method teachings. Legal theory sheds light upon the instruments of establishment and application law, e.g. over the linguistic function of legal norms.

One can characterise philosophy of law in relation to other disciplines as follows: unlike inquiries into valid law it is concerned with the law not from an internal user perspective, but from an external perspective. Unlike other basic areas of jurisprudence, for example, history of law or legal sociology this perspective is not simply descriptive but comprehensive and thus normative (i.e. prescriptive as well as valid) and analytic.

On account of posing questions regarding normativity and justification, legal ethics is a part of general ethics and thus of general philosophy. On account of posing questions of a comprehensive, philosophical nature legal theory is a part of other philosophical sub-disciplines, such as theory of action, logic, philosophy of language and epistemology and thus general philosophy. Philosophy of law differs from other philosophy disciplines on account of its object of investigation

Philosophy of law with its two subsections of legal ethics and legal Theory takes a hermaphrodite position between philosophy and jurisprudence - or at least ought to. The separation from the other sub-disciplines of philosophy and jurisprudence is facilitated through the element which at the same time allows philosophy of law to be part of each of the subjects. Law's subject of investigation allows philosophy of law to belong partially to jurisprudence and at the same time distinguishes it from the other sub-disciplines of philosophy. The philosophical method of investigation allows philosophy of law to belong partially to philosophy and at the same time distinguishes it from the other sub-disciplines of jurisprudence.

This peaceful scene of reasonable division of labour between legal ethics and legal theory as sections of philosophy of law, which is itself a sub-discipline within both philosophy and jurisprudence, only partly describes the conditions as they stand today. If one turns one’s eyes towards the historical development of the discipline then the scene is not so peaceful and instead characterised by endeavours towards expansion, containment and displacement.
After natural law (1) had dominated wide sections of practical philosophy in the 17th and 18th centuries as forerunner of philosophy of law (2), Hegel wanted his "Grundlinien der Philosophie des Rechts" [Elements of the Philosophy of Right] of 1821 to set Law in relationship to a comprehensive, philosophical world building. This high standard for philosophy of law was fostered in Germany in particular and has been maintained by many throughout 19th and 20th Centuries - in that period in which philosophy was dethroned from her position as "Queen of the Sciences". In this period different counter-movements can already be detected. New subjects such as "legal doctrine", "legal theory", "constitutional law" and "political science" signal the radical break from the high standards of philosophy of law and natural law and the veering towards the other extreme, towards legal positivism (3). At the same time not only was the ambitious demand to set law in relationship to the whole of  philosophy rejected, but also the more moderate demand of connecting legal ethics to practical philosophy but with a reduced metaphysical element. From now on "science must be unbiased" was the credo. For some, only a description and analysis of existing law and its general structures were permitted, i.e. only legal theory.

In post-1945 Germany the collapse of both the political order and the weltanschauung of many people as well as the erroneously blaming of  legal positivism for the helplessness of German lawyers in the face of the dictatorship, led to a short Renaissance of natural law and thus philosophy of law in its most ambitious form. Papers on topics such as "Law and Time" were written and the increasing scepticism in other countries and other academic subjects concerning excessive metaphysical requirements was overlooked, a scepticism which spread to the substantive law academics within law.

In the late 60’s, the 70’s and 80’s this natural law intellectual flight of fancy was followed by disillusionment and a veering off to the other extreme. With approximately 20 to 30 years delay many oriented themselves towards the positivistic ideal which was en vogue in the Anglo-Saxon sphere (especially among those German-speaking emigrants such as Wittgenstein, Carnap, Kelsen and Popper) in the 30’s, 40’s and 50’s. If one did not completely limit oneself to inquiries into valid law, then one now pursued legal theory, legal norms theory, legal logic, language analysis, rhetoric, argumentation theory, term analysis, and legal sociology. The philosophy of law ought to be replaced by legal theory and legal sociology. Others engaged only in the historical aspects and dedicated themselves to the interpretation of classical authors of legal philosophy. This development began almost exactly at that point in time when the doubtfulness of the clean separation of descriptive and normative language as well as language analysis as the foundation of all thinking was recognised in the Anglo-Saxon tradition and the move in the opposite direction towards a topic oriented practical philosophy and ethics began. political philosophy in particular experienced a renaissance in the Anglo-Saxon world at the end of the 60’s and beginning of the 70’s and is linked with names such as Rawls, Nozick and Dworkin. While many professional philosophers in Germany have recognised the consequences of this new development little notice has been taken among lawyers. This, one would almost like to say "typically German", to-ing and fro-ing between excessively high standards and complete rejection of philosophy of law paired with great disillusionment has negatively affected its acceptance among colleagues concerned with substantive law.

(1) "Natural law" is used to denote the view that there exist "super-positive" "natural" norms which man-made laws orientate themselves towards.

(2) On the development of the term "philosophy of law" see Dietmar von der Pfordten "Die Entwicklung des Begriffs "Rechtsphilosophie" vom 17. Bis zum Anfang des 19. Jahrhunderts" in "Archiv für Begriffsgeschichte" 41, (1999) pp 151-161

(3) "Legal positivism" is used to denote the view that beyond the positive law created by humans there is no measure of justice.