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How does section 109 of the Constitution resolve inconsistency between Commonwealth and state laws?

section 109 of the Australian Constitution and its significance for the division of powers

A focused VCE Unit 4 answer to section 109 of the Constitution. Covers the three forms of inconsistency, the consequence (invalidity of the state law to the extent of inconsistency), and the leading cases including the Engineers Case and Commonwealth v Australian Capital Territory (2013).

Generated by Claude Opus 4.86 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking

VCAA wants you to explain how section 109 of the Constitution resolves conflict between Commonwealth and state laws. Expect a 5-8 mark medium response in Section A or B.

The answer

The text

Section 109 of the Constitution of the Commonwealth of Australia provides:

When a law of a State is inconsistent with a law of the Commonwealth, the latter shall prevail, and the former shall, to the extent of the inconsistency, be invalid.

This is the rule of Commonwealth supremacy in concurrent areas of legislative power.

The three forms of inconsistency

The High Court has identified three forms of inconsistency.

1. Direct inconsistency: simultaneous obedience impossible. The state law and Commonwealth law impose directly contradictory obligations. Example: a state law that requires conduct the Commonwealth law prohibits.

2. Direct inconsistency: state law alters, impairs or detracts from the Commonwealth law. Even where simultaneous obedience is possible, the state law diminishes the operation of the Commonwealth law (Clyde Engineering Co Ltd v Cowburn (1926) 37 CLR 466).

3. Indirect (cover the field) inconsistency. The Commonwealth law manifests an intention to cover the field exhaustively. Any state law in that field is inconsistent. (Ex parte McLean (1930) 43 CLR 472.)

The consequence

The state law is invalid "to the extent of the inconsistency". This is a partial, not total, invalidation: only the inconsistent portion is struck down. If the inconsistent Commonwealth law is later repealed, the state law revives.

Leading cases

Amalgamated Society of Engineers v Adelaide Steamship Co Ltd (1920) 28 CLR 129 (the Engineers Case). The Engineers Case reset constitutional interpretation. The High Court rejected the doctrines of reserved state powers and implied intergovernmental immunities, holding that Commonwealth laws made under s 51 powers applied to state-owned enterprises. This established the modern approach: Commonwealth heads of power are interpreted on their natural meaning and prevail under s 109 in areas of concurrent power.

McBain v Victoria (2000) 99 FCR 116; Re McBain; Ex parte Australian Catholic Bishops Conference (2002) 209 CLR 372. The Federal Court found a Victorian law restricting IVF to married women was inconsistent with the Sex Discrimination Act 1984 (Cth). The relevant Victorian provision was invalid to the extent of the inconsistency.

Commonwealth v Australian Capital Territory (2013) 250 CLR 441. The High Court struck down the Marriage Equality (Same Sex) Act 2013 (ACT) on the ground that the Marriage Act 1961 (Cth) (as it then stood) was intended to cover the field of marriage. The ACT Act could not operate concurrently. (The Commonwealth subsequently amended the Marriage Act 1961 (Cth) to recognise same-sex marriage in 2017.)

Significance for the division of powers

The Australian Constitution distributes legislative power between the Commonwealth and the states. The states have plenary legislative power; the Commonwealth has enumerated powers under s 51 (and a few other heads). Most s 51 powers are concurrent (both can legislate). Section 109 is the device that resolves the conflict where both have legislated.

The practical effect over time has been steady expansion of Commonwealth law into areas formerly dominated by state law, particularly through:

the external affairs power (s 51(xxix)), used to implement international treaties (e.g. the Commonwealth v Tasmania (1983) 158 CLR 1 (the Tasmanian Dam case));
the corporations power (s 51(xx)) (e.g. the WorkChoices case, New South Wales v Commonwealth (2006) 229 CLR 1);
the financial corporations power and the taxation power.

The limits of section 109 as a check

Section 109 is powerful but conditional. It only bites where there is an actual clash between a valid Commonwealth law and a valid state law. Where the Commonwealth has not legislated in a concurrent area, the state law stands; where a matter falls within exclusive state power (most criminal law, property and land law, local government), there is no Commonwealth law to be inconsistent with, so s 109 never operates. The invalidity is also partial: only the inconsistent portion of the state law is struck down, and the state law revives if the Commonwealth law is later repealed. A high-band answer treats s 109 as a targeted resolution rule for concurrent powers, not a general statement that the Commonwealth always wins.

Applying section 109 to a stimulus

Question: A Commonwealth Act sets a national workplace safety standard and states an intention to regulate the field exhaustively. A state then passes a stricter standard for the same workplaces. Explain whether and how s 109 applies.

Step 1: Confirm both laws are valid

Assume the Commonwealth law is supported by a head of power (for example the corporations power) and the state law is within state plenary power. Section 109 only applies between two valid laws.

Step 2: Identify the form of inconsistency

Even though a business could obey both by meeting the stricter state standard, the Commonwealth law evinces an intention to cover the field. Under the cover-the-field test (Ex parte McLean), any state law operating in that field is inconsistent, so this is indirect inconsistency.

Step 3: Apply the consequence in s 109

The state law is invalid to the extent of the inconsistency. Because the Commonwealth intended to occupy the whole field, the state standard cannot operate in that field while the Commonwealth law stands.

Step 4: Note the conditional nature

If the Commonwealth later repealed its standard, the state law would revive. The invalidity is partial and depends on the continuing operation of the Commonwealth law.

Exam-style practice questions

Practice questions written in the style of VCAA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

2024 VCAA8 marksExplain the operation of section 109 of the Constitution and the way it has been applied by the High Court.

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An 8-mark response needs the text of s 109, the three forms of inconsistency, the consequence, and at least two leading cases.

Text. Section 109 of the Constitution provides: "When a law of a State is inconsistent with a law of the Commonwealth, the latter shall prevail, and the former shall, to the extent of the inconsistency, be invalid."

Three forms of inconsistency.

Direct inconsistency: simultaneous obedience impossible. The state law and Commonwealth law contradict each other directly. Example: a state law banning conduct the Commonwealth requires.
Direct inconsistency: state law alters, impairs or detracts from the Commonwealth law. Even where simultaneous obedience is possible, the state law impairs the Commonwealth law (Clyde Engineering Co Ltd v Cowburn (1926) 37 CLR 466).
Indirect (cover the field) inconsistency. The Commonwealth law evinces an intention to cover the field exhaustively, so any state law operating in that field is inconsistent (Ex parte McLean (1930) 43 CLR 472).

Consequence. The state law is invalid "to the extent of the inconsistency". The state law revives if the Commonwealth law is later repealed.

Leading cases.

Amalgamated Society of Engineers v Adelaide Steamship Co Ltd (1920) 28 CLR 129 ("Engineers Case") confirmed Commonwealth supremacy in areas of concurrent legislative power.
Commonwealth v Australian Capital Territory (2013) 250 CLR 441 struck down the Marriage Equality (Same Sex) Act 2013 (ACT) on the ground that the Marriage Act 1961 (Cth) covered the field.

Markers reward the exact words of s 109, the three forms with case authority, and the consequence stated precisely.

VCAA 20225 marksExplain the significance of section 109 of the Constitution as a check on state lawmaking power, and discuss one limitation on its operation.

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A 5-mark explain-and-discuss item rewards the role of s 109 in the division of powers, plus a genuine limit.

Significance. The states have plenary legislative power, but most Commonwealth heads of power under s 51 are concurrent (both can legislate). Section 109 resolves any clash by making the state law invalid to the extent of the inconsistency, with the Commonwealth law prevailing. It therefore acts as a check on state power in concurrent areas and, over time, has allowed steady expansion of Commonwealth law (for example through the external affairs power in the Tasmanian Dam case).

Limitation. Section 109 only operates where there is an actual inconsistency between a valid Commonwealth law and a valid state law. It does not apply where the Commonwealth has not legislated, or where the matter is within exclusive state power, so the states retain full control of large areas (for example most criminal law and land law). The state law is also only invalid to the extent of the inconsistency and revives if the Commonwealth law is repealed, so the check is partial and conditional, not a general grant of Commonwealth supremacy.

Markers reward the concurrent-powers context, the check on state power, and a precise limitation (no Commonwealth law means no s 109 operation; partial and revivable invalidity).