In 'Applied Jurisprudence and Principles of Legal Practice' Albert Keating argues that substantive jurisprudence may be extended to include concepts of applied jurisprudence and principles of legal practice. He advances his argument by asserting that the first task of applied jurisprudence is to identify the basic law of the constitution of a legal system by the application of naturalist and positivist principles. The second task is to identify the sources of law at play in the system, and this includes interpretative sources, which may be ranked as primary, secondary and tertiary sources of law. Interpretative sources also consist of tests and criteria formulated by the courts out of former decisions, and applied to current contentious matters of the same kind. The jurisprudential process of conceptualisation may also be adopted and applied when formulating concepts out of a fusion of rules, duties and rights, and illustrates this by a formulating a concept of a will fashioned out of a fusion of the validity rules of wills, duties of executors and succession rights of beneficiaries. Determinant factors may also be employed for the purposes of devising formulae for use in legal practice, and for identifying the correct legal procedures for use in applications to the courts.