Characterisation and heads of power 

The Commonwealth Parliament has no general legislative power. It may make laws only on the subjects the Constitution enumerates, so every question about a Commonwealth law begins in the same place: is this law supported by a head of power at all?² That question is called characterisation, and it is logically prior to every prohibition — a law that no power supports is invalid whether or not it also offends s 92 or the implied freedom.

What the question is, and what it is not

Characterisation asks whether the law answers the description of a granted power. It does not ask whether the law is wise, fair, or well drafted. Those are questions for the Parliament, and the High Court has said so repeatedly.

Two habits keep the analysis clean:

• Name the placitum. "The corporations power" is not an answer; s 51(xx) and its terms are. The words of the grant do the work.
• Separate characterisation from limitation. Characterisation asks whether power exists. Limitations — s 92, s 51(xxxi)'s just terms, Chapter III, the implied freedom, and the limit on laws that single out or burden the States, from Melbourne Corporation v Commonwealth (1947) 74 CLR 31³ — ask whether an existing power has been exercised impermissibly. Running the two together produces a muddled answer.

Non-purposive powers: sufficient connection

Most heads of power in s 51 are expressed as subject matters — trade and commerce, corporations, external affairs, taxation. For these, the settled approach was restated in Grain Pool of Western Australia v Commonwealth (2000) 202 CLR 479:¹

• The question is whether the law is with respect to the subject matter, which requires a sufficient connection between the law and the head of power.
• The connection must be more than insubstantial, tenuous or distant.
• The court looks to the law's practical operation as well as its legal operation — what the law actually does, not what it is called.
• Motive is irrelevant. That Parliament passed a taxation law hoping to discourage an activity does not stop it being a law with respect to taxation.
• The power is construed with all the generality the words admit, and is not narrowed by reference to what the States might otherwise do.

The threshold is therefore undemanding. A law with a real connection to an enumerated subject will generally be supported, and most constitutional argument is really about the reach of the subject rather than the strength of the connection.

Purposive powers

A few powers are expressed as purposes rather than subjects — most importantly the defence power in s 51(vi), and the incidental power in s 51(xxxix).

For these the test differs. The question is whether the law is reasonably capable of being considered appropriate and adapted to achieving the stated purpose. That imports a proportionality-style inquiry that has no place in characterising a subject-matter power.

The defence power is also elastic: its scope expands in wartime and contracts in peace, so the same law may be supported at one time and not another. Characterisation of a purposive power therefore depends on the factual circumstances in a way that subject-matter characterisation does not.

The incidental scope of a power

Every grant carries with it power to legislate on matters incidental to its subject — the enforcement, machinery and ancillary provisions without which the power could not be exercised effectively. This is implied into each grant, and s 51(xxxix) supplies an express incidental power in addition.

Incidental scope explains why a law that does not itself operate on the subject may still be valid: an offence provision, a record-keeping requirement, or a rule about proof attached to a valid scheme is supported as incidental to it.

Dual characterisation

A law may answer the description of more than one head of power, and it is enough that it answers one. The Commonwealth need not nominate a single source, and a court that finds one sufficient power need go no further.

The corollary matters more. A law is not invalid because it also operates on a subject reserved to the States or outside Commonwealth power. The reserved powers doctrine — that s 51 grants should be read down to preserve State legislative fields — was rejected in Engineers and has never been revived. A law within a granted power is valid even though its subject overlaps with State concerns.

Reading down and severance

A law that goes beyond power is not always wholly invalid. Two techniques save what can be saved.

Reading down construes a provision, where its words fairly permit, as confined to what the power supports. Commonwealth interpretation legislation directs that a law be read as operating to the full extent of, but not beyond, legislative power. The limit is that the reading must be one the text can bear — a court will not rewrite a provision to rescue it.

Severance removes the invalid part and leaves the rest standing, provided what remains is capable of independent operation and the Parliament would have enacted it alone. Where the invalid element is so entwined that the remainder would operate differently from what was intended, the whole falls.

Both are questions of construction and legislative intention, not discretion, and both come after characterisation has shown a defect.

The reach of external affairs

Section 51(xxix) deserves separate mention because it is the widest of the subject-matter powers and the one most often raised where no other power fits.

It supports laws implementing a treaty Australia has entered, provided the law is reasonably capable of being considered appropriate and adapted to implementing the obligation, and the treaty is bona fide rather than a device. It also supports laws on matters geographically external to Australia, and on matters of international concern.

Its breadth is what makes characterisation matter so much in practice: a Commonwealth law with no obvious domestic head of power may still be valid if an international obligation supports it, which is why the treaty basis should be examined rather than assumed absent.

Applying this in a problem question

1. Identify the impugned law and, precisely, the provisions in issue.
2. Nominate the head of power and quote the placitum, then construe its words.
3. For a subject-matter power, test sufficiency of connection by reference to the law's practical operation, and say what that operation is.
4. For a purposive power, apply the appropriate-and-adapted test instead, and address the factual circumstances the purpose depends on.
5. Consider the incidental scope where the provision is machinery rather than substance.
6. If one power fails, try another — dual characterisation means the Commonwealth needs only one.
7. Only then turn to limitations, and treat each as a separate question.

Self-check

• Have I named the placitum rather than the power's nickname?
• Have I kept characterisation separate from constitutional prohibitions?
• Have I used the right test for the kind of power?
• Have I looked at practical operation rather than the law's label?
• Have I avoided reasoning that a State field narrows a Commonwealth grant?