One of the oldest principles of the rule of law is that citizens should be able to determine, with reasonable certainty, what conduct is prohibited by criminal legislation. This is particularly important where the consequences of getting the answer wrong include a substantial fine or imprisonment. Yet South Australia's machete prohibition raises a surprisingly difficult question: what exactly is a knife? The answer is not merely of academic interest. It may determine whether a rural property owner can lawfully purchase and use an ordinary agricultural implement that has existed for centuries.
From 1 July 2025, South Australia classified machetes as prohibited weapons under its amended weapons legislation. Section 21F of the Summary Offences Act 1953 provides for a maximum penalty of $20,000 or two years' imprisonment for relevant offences involving prohibited weapons, subject to statutory exemptions. The government's stated objective was to reduce knife-related violence. Few reasonable people would dispute the desirability of preventing violent criminals from carrying dangerous weapons in public. But the legislation reaches beyond that problem into the ordinary possession, use and commercial supply of objects whose legal classification may be far from obvious.
Regulation 6 of the Summary Offences Regulations 2016 defines a machete as "a large knife designed or adapted for use as an agricultural slashing tool or weapon." The wording appears straightforward until one begins examining what it actually means. There is no fixed blade-length threshold, no requirement that the object resemble a conventional machete, and no express exclusion for traditional agricultural cutting implements. Instead, criminal liability can turn upon the interpretation of two ordinary English words: "large" and "knife."
The most revealing feature of the definition is not the adjective "large," although that is vague enough. It is the relationship between the word "knife" and the remainder of the definition. The prohibited object must be a large knife designed or adapted for agricultural slashing or use as a weapon. But agricultural slashing is precisely the function of numerous traditional tools, including billhooks, brush hooks, cane knives and other specialised cutting implements. The agricultural qualification does not exclude these tools. On the contrary, it identifies the very activity for which many of them were designed.
This leaves the word "knife" carrying almost the entire burden of distinguishing prohibited machetes from ordinary agricultural equipment. And that word is far less precise than legislators may have imagined.
Consider the traditional billhook. This is an agricultural and forestry implement with a substantial curved blade, frequently ending in a hook, fitted to a wooden handle. It is used for clearing scrub, cutting woody vegetation, trimming branches and managing overgrown land. Some versions have relatively short handles, while others are mounted on longer shafts. Their shapes vary according to regional traditions and intended tasks. The billhook is not a modern invention or an improvised weapon. It is a familiar tool with a long history of legitimate agricultural use.
Is it nevertheless a knife? The answer is not obvious. Dictionaries and tool catalogues sometimes describe billhooks as hooked knives or heavy knives with curved blades. Such descriptions make it difficult to insist that the ordinary meaning of "knife" necessarily excludes them. At the same time, the billhook has an established identity as a specialised agricultural implement, distinct from the conventional machete. Both descriptions may be linguistically defensible, which is precisely the difficulty when criminal liability depends upon the classification.
The sickle presents another problem. It has a curved cutting blade and a handle, and its purpose is to cut vegetation. Yet it is ordinarily classified as a harvesting implement rather than a knife. A sharpened spade can cut roots, while a hoe can slash vegetation. Neither would normally be described as a knife. A sharpened flat steel bar might possess a cutting edge without acquiring the customary identity of a knife. The mere ability to cut cannot be sufficient, or the definition would threaten to expand across much of the agricultural tool shed.
The kukri, by contrast, demonstrates why blade curvature cannot resolve the question. This traditional Nepalese implement has a distinctive forward-curved blade and is commonly classified as a knife. It can perform agricultural and utility functions as well as serve as a weapon. A substantial kukri might therefore fall within the South Australian machete definition notwithstanding its shape and traditional identity. The same general function can be performed by objects belonging to different customary categories, while objects within a single category may have markedly different physical designs.
Nor does the word "large" provide much assistance. Large compared with what? A pocketknife, a kitchen knife, a hunting knife or a conventional machete? A blade of 19 centimetres does not automatically escape the South Australian definition, and a blade of 21 centimetres does not automatically satisfy it. South Australia chose a qualitative description rather than a fixed numerical threshold. That leaves considerable room for disagreement about objects near the boundary.
These are not imaginary philosophical puzzles. They arise from the actual wording of a criminal prohibition. A property owner contemplating the purchase of a replacement billhook head may have to ask whether the detached blade is itself a knife, whether its intended handle affects the classification, and whether its established agricultural purpose brings it within the prohibition rather than taking it outside. The fact that such questions can reasonably be asked reveals a serious problem with the legislation.
A court could eventually resolve a particular dispute by considering the text, context and purpose of the regulations, together with the object's design and customary classification. But that does not solve the problem facing the ordinary citizen before purchasing the implement. Criminal legislation should provide reasonable guidance before a person acts, not merely offer the possibility of clarification after prosecution.
The statutory exemptions make the situation more revealing. Schedule 2 of the Summary Offences Act contains exemptions for particular circumstances, including specified business or employment purposes. The 2025 amending legislation also inserted clause 25, providing an exemption relating to machetes used or possessed for gardening or camping. The precise commencement status of that provision must be distinguished from its enactment, since a provision appearing in an amending Act is not necessarily operative immediately.
The existence of the gardening and camping provision is significant regardless of that commencement question. Parliament plainly recognised that objects falling within the machete category can have ordinary, innocent uses. It therefore sought to protect at least some such activities through an exemption. This is not conclusive proof that every billhook is legally a machete, but it demonstrates the underlying difficulty of prohibiting a category of objects that overlaps with legitimate agricultural and domestic equipment.
The legislative method is to prohibit broadly and then create exceptions for particular purposes. That may be administratively convenient, but it places an additional burden upon citizens who must determine whether they are covered by an exemption. The ordinary landowner is no longer concerned solely with whether an implement is dangerous or whether he intends to misuse it. He must also consider whether his particular activity falls within the statutory language.
What counts as gardening? Clearing blackberry growth around a farmhouse may comfortably fit the ordinary meaning. But what about clearing a creek line, removing woody weeds from a rural property, maintaining a firebreak, conducting bush regeneration or participating in a volunteer Landcare project? Some of these activities might reasonably be characterised as gardening or land maintenance, while others are less clearly covered. The uncertainty is not necessarily eliminated by pointing to an exemption whose own boundaries require interpretation.
The business and employment exemptions raise similar questions. A professional agricultural worker may have a relatively straightforward basis for arguing that a cutting implement is reasonably required for employment. But a retired person maintaining a rural holding, or a property owner undertaking unpaid fire-prevention work, may not fit comfortably within that category. The legitimacy of the activity does not automatically establish the availability of a particular statutory defence.
Section 21F(2) adds another important dimension. It provides that it is a defence for the defendant to prove that he or she was an exempt person in relation to the prohibited weapon. This is a significant departure from the ordinary expectation that the prosecution bears the burden of establishing criminal guilt. The prosecution must still prove the elements of the offence, including that the object falls within the legally prohibited category. But where the defendant relies upon the statutory exemption, the provision places a persuasive burden upon that person.
The practical implications should not be underestimated. An ordinary property owner may believe that his use of a cutting implement is entirely legitimate. Yet if police classify the object as a machete and proceedings follow, he may have to establish the relevant exemption in court. Even a successful defence can involve inconvenience, expense, anxiety and the disruption of ordinary life.
The rule of law is not fully vindicated merely because an innocent defendant may eventually be acquitted. A system in which ordinary citizens must defend themselves against criminal charges to establish their entitlement to use familiar agricultural tools imposes costs that should be considered when legislation is drafted.
The restrictions upon exemptions for persons with specified criminal histories introduce further complications. Schedule 2 clause 2 contains disqualification provisions affecting access to exemptions in certain circumstances. The precise operation depends upon the relevant conviction, statutory criteria and applicable exceptions. The broader point is that the legality of possessing an agricultural implement may depend not only upon its design and intended use but also upon the personal legal history of its owner.
Restrictions upon dangerous individuals can be justified in appropriate circumstances. Nevertheless, there is a substantial difference between prohibiting the possession of weapons for threatening or violent purposes and preventing a person from using an ordinary agricultural cutting implement for legitimate work. Where a law reaches the latter situation, proportionality deserves serious examination.
The most important practical consequence of the machete prohibition may never appear in a courtroom. It may instead emerge through the behaviour of importers, wholesalers and retailers.
Consider a supplier contemplating the importation of traditional billhook replacement heads. The market is relatively small. The legal classification is uncertain. Supplying a prohibited weapon without satisfying the relevant legal requirements can attract serious penalties. The legislation also imposes conditions upon persons dealing in prohibited weapons, including notification and record-keeping requirements in relevant circumstances.
What is the rational commercial response? The supplier may simply decide that the product is not worth the legal risk. A retailer may remove it from the catalogue. An importer may decline to order another shipment. The customer looking for a replacement agricultural blade may discover that it is no longer readily available, not because a court has determined that it is prohibited, but because businesses are unwilling to finance a legal argument about the meaning of "knife."
This is the chilling effect of uncertain criminal regulation. The law need not be successfully prosecuted against every borderline object. It need only create sufficient doubt that cautious businesses withdraw from the market. In this way, an ambiguous prohibition may produce a practical restriction wider than anything Parliament expressly specified.
The effect is particularly serious for specialised agricultural equipment. Large manufacturers selling thousands of products may have legal departments capable of assessing regulatory risks. Small importers and rural suppliers often do not. They are unlikely to spend substantial sums litigating the classification of an obscure cutting implement with modest sales. Commercial caution may therefore eliminate products whose legality has never been judicially determined.
This is not evidence that a particular retailer has already withdrawn billhooks because of the South Australian law. That would require specific commercial evidence. It is, however, a foreseeable mechanism through which legal uncertainty can restrict supply. The burden falls upon the ordinary user, who may have little practical opportunity to challenge the classification.
The problem illustrates a broader weakness in modern regulatory criminal law. Governments increasingly attempt to prevent harmful behaviour by prohibiting categories of objects, rather than concentrating primarily upon the circumstances in which those objects are possessed or used. The approach is politically attractive because it produces visible results. Ministers can announce a ban, publicise surrender arrangements, display confiscated items and claim to have taken decisive action.
But the existence of a prohibited category does not establish that the underlying causes of violence have been addressed. Criminal violence involves human conduct, intentions and social circumstances. Gang disputes, intimidation, assaults and the carrying of weapons in public cannot be explained simply by the availability of a particular agricultural blade.
An axe can inflict fatal injuries. So can a hammer, a crowbar, a kitchen cleaver or a sharpened gardening implement. Yet society does not generally treat the ordinary possession of all potentially dangerous tools as criminal. The law must draw distinctions, and those distinctions should be based upon coherent principles rather than the political visibility of particular objects.
A more defensible approach would place greater emphasis upon threatening conduct, unlawful carrying in public, possession for criminal purposes and the misuse of weapons. Such laws are not without difficulties, and South Australia already has offences addressing aspects of dangerous conduct. But regulating behaviour more directly can avoid unnecessarily burdening people who possess ordinary tools for legitimate work.
The distinction is particularly relevant to rural Australia. A suburban politician may regard a substantial curved blade as an alarming object. A farmer, orchardist or rural property owner may recognise it immediately as a useful implement for clearing vegetation. The same physical object can have very different practical significance depending upon the circumstances in which it is encountered.
The law should not assume that the ordinary tools of rural life are inherently suspicious merely because they resemble objects that have sometimes been used in violent offences. Nor should the citizen's ability to continue using such tools depend unnecessarily upon discretionary interpretation by police officers, prosecutors or administrative authorities.
There is a philosophical issue here that reaches beyond the machete prohibition. Lon Fuller, in The Morality of Law, identified clarity and congruence between official rules and their administration among the requirements of a functioning legal order. Laws should not merely exist as commands on paper. They should provide intelligible guidance capable of being followed in ordinary life, and their administration should correspond reasonably closely to their declared meaning.
The South Australian legislation invites examination under those principles. The statutory prohibition identifies a broad category of objects. Exemptions protect specified activities, subject to their operative terms and conditions. Police guidance attempts to explain the practical consequences. But the citizen must still reconcile the statutory definition, the exemptions and the possible interpretation of enforcement authorities.
These are not necessarily three contradictory laws, but they can produce three different levels of practical understanding. The statute declares a prohibition. Administrative guidance explains circumstances in which possession may be permitted. The individual citizen must then determine whether his particular implement and activity fall within the permitted category. Where the boundary is uncertain, practical security may depend heavily upon enforcement discretion.
Discretion is unavoidable in policing, but it should not become a substitute for clear legislation. The fact that an officer is unlikely to prosecute a rural landowner for using a traditional billhook does not establish that the landowner's legal position is satisfactory. A citizen should be able to rely upon the law itself, rather than upon an expectation that officials will exercise common sense.
Nor does the existence of statutory exemptions necessarily cure an overbroad prohibition. Exemptions may be essential to prevent unjust outcomes, but they can also make the law increasingly complicated. Each exemption creates questions about eligibility, conditions, proof and interpretation. The result may be a system in which lawful conduct is technically preserved while becoming progressively more difficult for ordinary people to navigate.
This is particularly troubling where the penalties are severe. Two years' imprisonment is not a trivial consequence. A criminal prohibition carrying such a maximum should be drafted with particular attention to the predictability of its application. The greater the potential punishment, the stronger the public interest in ensuring that citizens can identify the prohibited conduct without elaborate legal analysis.
There are straightforward ways to improve the legislation. Parliament could expressly clarify the status of traditional agricultural implements such as billhooks, sickles and brush hooks. It could provide more objective criteria for distinguishing machetes from other cutting tools. It could address the position of replacement heads and components. It could also ensure that legitimate rural land management, volunteer conservation and fire-prevention activities are adequately protected by clearly operative exemptions.
None of these changes would require the government to abandon its concern about knife violence. The objective should be to distinguish more accurately between criminal misuse and ordinary lawful activity. Better drafting could strengthen the legitimacy of the prohibition by ensuring that it reaches the conduct and objects Parliament actually intends to regulate.
The humble billhook provides an unusually revealing test case because its innocent agricultural function is so obvious. It has existed for generations as a tool for clearing vegetation. Its distinctive shape and customary identity distinguish it from the conventional machete, yet dictionary descriptions and the broad statutory language leave room for argument about whether particular designs are legally large knives.
That uncertainty may never be resolved by a reported judicial decision. There may be too little commercial incentive for a retailer to challenge the law and too much personal risk for an individual to invite prosecution. The absence of litigation would not necessarily demonstrate that the legislation is clear. It might instead demonstrate that the cost of testing it is too high.
This is how uncertain criminal legislation can extend its practical influence beyond the cases that Parliament or the courts have expressly considered. Importers become cautious, retailers withdraw products, and ordinary citizens abandon activities or purchases rather than risk legal trouble. The chilling effect can operate silently, without convictions or even prosecutions.
The deeper question is whether modern criminal law is still expected to describe prohibited conduct with reasonable precision, or whether increasingly broad categories are being created and their boundaries left to administrative interpretation and individual risk assessment.
The law does not need to win a prosecution against the billhook. It needs only to make the importer unwilling to stock it, the retailer unwilling to sell it, and the landowner unwilling to purchase it. At that point, an ambiguous criminal prohibition may have achieved through commercial caution what Parliament never clearly commanded.
A society governed by the rule of law should demand better. Criminal legislation should not require a farmer, gardener or rural property owner to obtain specialist legal advice before purchasing a familiar vegetation-clearing implement. Nor should the ordinary citizen's security depend upon the hope that police and prosecutors will interpret an uncertain definition sympathetically.
The question is no longer merely when a knife is not a knife. It is whether the criminal law should be permitted to regulate ordinary life through uncertainty, leaving citizens to discover the boundaries of legality at their own expense.
That is not a satisfactory foundation for the rule of law. It is government by prohibition, exception and discretion, where the individual is expected to bear the consequences of Parliament's failure to say clearly what it means.