In Fencott [(1983) 152 CLR 570 at 608 per Mason, Murphy, Brennan and Deane JJ] it was said that 'in the end, it is a matter of impression and of practical judgment whether a non-federal claim and a federal claim joined in a proceeding are within the scope of one controversy and thus within the ambit of a matter'. The references to 'impression' and 'practical judgment' cannot be understood, however, as stating a test that is to be applied. Considerations of impression and practical judgment are relevant because the question of jurisdiction usually arises before evidence is adduced and often before the pleadings are complete. Necessarily, then, the question will have to be decided on limited information. But the question is not at large. What is a single controversy 'depends on what the parties have done, the relationships between or among them and the laws which attach rights or liabilities to their conduct and relationships' [ Fencott (1983) 152 CLR 570 at 608 per Mason, Murphy, Brennan and Deane JJ]. There is but a single matter if different claims arise out of 'common transactions and facts' or 'a common substratum of facts' [ Philip Morris (1981) 148 CLR 457 at 512 per Mason J], notwithstanding that the facts upon which the claims depend 'do not wholly coincide' [ Fencott (1983) 152 CLR 570 at 607 per Mason, Murphy, Brennan and Deane JJ]. So, too, there is but one matter where different claims are so related that the determination of one is essential to the determination of the other [ Philip Morris (1981) 148 CLR 457 at 512 per Mason J], as, for example, in the case of third party proceedings or where there are alternative claims for the same damage and the determination of one will either render the other otiose or necessitate its determination. Conversely, claims which are 'completely disparate' [ Felton v Mulligan (1971) 124 CLR 367 at 373 per Barwick CJ], 'completely separate and distinct' [ Philip Morris (1981) 148 CLR 457 at 521 per Murphy J] or 'distinct and unrelated' [ Moorgate Tobacco Co Ltd v Philip Morris Ltd (1980) 145 CLR 457 at 482 per Stephen, Mason, Aickin and Wilson JJ] are not part of the same matter."
18 Once a matter is within federal jurisdiction [in relation to the instant proceedings under Part IV of the TPA], the entirety of the matter is a matter in federal jurisdiction being the justiciable controversy between the actors to it comprised of the substratum of facts representing or amounting to the dispute or controversy between them. As Allsop J observed, this wholly federal matter is not 'the cause of action' and is identifiable independently of 'the proceeding' or 'proceedings brought for its determination': Fencott at 603-608; ASIC v Edensor Nominees Pty Ltd (2001) 204 CLR 559 at [2]
19 In the same article the learned author under the heading "Once federal, only and ever federal", observed as follows [at 13]: