Thus, the Indian Penal Code is substantive, as it lays down what acts amount to various offences, and prescribes the corresponding punishments. The Criminal Procedure Code, on the other hand, is procedural, for it furnishes the detailed machinery for trying offenders. This procedure is to be followed for trying all criminal offences under the Indian Penal Code.
The same procedure also applies to offences under any other law, unless any enactment prescribes a special form of procedure applicable to such offences (S. 4). Thus, special or local laws in force in India are not affected by the Criminal Procedure Code. (S. 5)
However, the Code is not wholly procedural or adjective in nature. There are several provisions in the Code which also confer substantive rights. Thus, S. 125 of the Code confers the right of maintenance on a wife or child; the Code also grants the right of Habeas Corpus; and a right of appeal is likewise available under the Code.
Not only does the Criminal Procedure Code supplement the substantive Criminal Law, by laying down rules or procedure mainly dealt with Chapters referring to Trials and sections referring to Appeals, Reference and Revision, but it also prescribe substantive rules for the prevention of offences. The Code also prescribes rules for the disposal of property. Hence the Code is not purely an adjective law or a law of procedure.
It may also be noted that procedural law is not, in any way, less important than substantive law. In fact, the two are equally important, and complement each other. In a given case, the substantive penal law may be a perfect combination of reason and wisdom, and yet, the worst criminals may escape through the flaws and loop-holes of the law of procedure. It is, therefore, imperative, that the procedural law should be as effectual as possible.