The state of knife carry laws in the United States is an unmitigated disaster.
In order for the law to be obeyed, it must be clear. Only about 14 states have blade length limits specified by statute, but anyone who thinks katana carry is legal in 36 states is in for a big surprise. This creates a problem, since pocketknives are usually not dangerous weapons, but no legal bright line exists separating them from katanas. In states that don't rely on a vague prohibition on "dangerous weapons", certain types of knives are typically named -- weapons such as "daggers", "dirks", "switchblades", or "gravity knives", none of which has a rigid definition. Some people consider dirk to be a generic term for knife, and flickable folders and balis are sometimes considered gravity knives.
There exist too many jurisdictions for bans on the carry of common cutting tools to be reasonable. No reasonable person can be expected to know the intricacies of even one state's laws, but anyone who travels must be aware of several sets of equally confusing laws. Between any pair of states, it's almost certain that there exists a knife legal in one but not in the other. States that allow cities and counties to make their own ordinances regarding knife carry worsen the situation; San Antonio, TX bans carry of any locking folder. Disparities in allowance of concealed or open carry are equally problematic. California statutes provide penalties primarily for concealed carry of certain blades, implying that open carry is respectable; yet Los Angeles bans open carry of knives over 3", despite the fact that California law allows concealed carry of folders of any length.
Society is too mobile for stark differences in knife carry restrictions to be reasonable. Travel between cities may not have been as common 100 years ago, but today, with airplanes and automobiles, nearly everyone makes regular trips to other jurisdictions, sometimes on short notice and to unfamiliar places. While this would be tolerable if all knives laws were uniform, the differences in knife laws can turn otherwise law-abiding citizens into criminals due to no overt act of their own. The same could be said of drug laws if they were they less uniform. There are very few or no other common tools whose owners are treated in such drastically different ways depending only on locational differences of a few feet.
The concealed versus open distinction tends to be controversial, in firearm carry discussions more that knife carry. The majority of Right to Bear Arms activists feel that open carry is more important than concealed carry, but nevertheless many states ban open carry of certain blades as well as firearms. As illustrated in the California and Los Angeles example above, cities tend to despise open carry of potential weapons. When states have chosen to ban or restrict concealed carry of firearms or knives and cities choose to restrict open carry, the combination presents a severe impediment to citizens' Right to Bear Arms. Particularly disturbing are instances where knives of common utility length -- say, less than 4" or 5" -- are restricted for both open and concealed carry, or are differently restricted depending on their mode of carry. Not only are citizens' RKBA restricted, but their ability to carry common tools is damaged in the name of protecting against criminals with weapons. Accidental concealment or revealing of even a common utility knife could result in criminal prosecution. This is all justified in the name of the government's ever-expanding "police power."
There is also the issue of case law, most problematic in states lacking clear blade length limits. The most serious problem with blade-related case law is that the vast majority of cases involve a defendant using a blade as a weapon. These cases bias Courts toward the view that knives are weapons and are bad. When they're presented with an allegedly upstanding citizen carrying a 4" knife, and a police officer who testifies that that 4" knife is primarily designed as a weapon, the logical conclusion is that this is yet another future criminal, and if they don't stop him now, he'll be back in court next year having stabbed someone in a bar-room brawl.
As mentioned above, cases not involving criminal misuse of a knife as a weapon are rare. In most states, there are fewer than a half a dozen cases that really provide valuable information about the legality of knives of particular kinds or lengths, cases that lack any ancillary criminal activity. There are usually even fewer cases -- only a couple -- that are citeable as a controlling authority declaring a knife to be legal; if you're unlucky, there will be no such cases, even for small knives. Cases of either type often hinge on whether the state's testimony would allow a reasonable jury to conclude that the knife in question was prohibited. In most cases, there is no exact description of the knife involved. Often, the length of the knife isn't even mentioned at the (state) Appeals or Supreme Sourt level. When state law doesn't draw any clear line between pocketknives as tools and folding knives as dangerous weapons, unless you get an activist conservative judge who will declare your knife ok as a matter of law, you're at the mercy of the jury -- the trier of fact -- to determine if your knife is a dangerous weapon.
Unless a state's law specifies a blade limit and doesn't leave the door open for illegal weapons less than that length (TX is one of a few that has clear laws, even though its 5.5" limit seems to suggest that legislators were trying to ban knives longer than a certain part of their anatomy), anything other than a SAK might theoretically result in arrest. There are a few states with [state] supreme court decisions which provide a clear length limit, and those limits are fairly safe. Still, nothing can stop supreme court judges from changing their mind, or new supreme court judges from having different views.
In order for the law to be obeyed, it must be clear. Only about 14 states have blade length limits specified by statute, but anyone who thinks katana carry is legal in 36 states is in for a big surprise. This creates a problem, since pocketknives are usually not dangerous weapons, but no legal bright line exists separating them from katanas. In states that don't rely on a vague prohibition on "dangerous weapons", certain types of knives are typically named -- weapons such as "daggers", "dirks", "switchblades", or "gravity knives", none of which has a rigid definition. Some people consider dirk to be a generic term for knife, and flickable folders and balis are sometimes considered gravity knives.
There exist too many jurisdictions for bans on the carry of common cutting tools to be reasonable. No reasonable person can be expected to know the intricacies of even one state's laws, but anyone who travels must be aware of several sets of equally confusing laws. Between any pair of states, it's almost certain that there exists a knife legal in one but not in the other. States that allow cities and counties to make their own ordinances regarding knife carry worsen the situation; San Antonio, TX bans carry of any locking folder. Disparities in allowance of concealed or open carry are equally problematic. California statutes provide penalties primarily for concealed carry of certain blades, implying that open carry is respectable; yet Los Angeles bans open carry of knives over 3", despite the fact that California law allows concealed carry of folders of any length.
Society is too mobile for stark differences in knife carry restrictions to be reasonable. Travel between cities may not have been as common 100 years ago, but today, with airplanes and automobiles, nearly everyone makes regular trips to other jurisdictions, sometimes on short notice and to unfamiliar places. While this would be tolerable if all knives laws were uniform, the differences in knife laws can turn otherwise law-abiding citizens into criminals due to no overt act of their own. The same could be said of drug laws if they were they less uniform. There are very few or no other common tools whose owners are treated in such drastically different ways depending only on locational differences of a few feet.
The concealed versus open distinction tends to be controversial, in firearm carry discussions more that knife carry. The majority of Right to Bear Arms activists feel that open carry is more important than concealed carry, but nevertheless many states ban open carry of certain blades as well as firearms. As illustrated in the California and Los Angeles example above, cities tend to despise open carry of potential weapons. When states have chosen to ban or restrict concealed carry of firearms or knives and cities choose to restrict open carry, the combination presents a severe impediment to citizens' Right to Bear Arms. Particularly disturbing are instances where knives of common utility length -- say, less than 4" or 5" -- are restricted for both open and concealed carry, or are differently restricted depending on their mode of carry. Not only are citizens' RKBA restricted, but their ability to carry common tools is damaged in the name of protecting against criminals with weapons. Accidental concealment or revealing of even a common utility knife could result in criminal prosecution. This is all justified in the name of the government's ever-expanding "police power."
There is also the issue of case law, most problematic in states lacking clear blade length limits. The most serious problem with blade-related case law is that the vast majority of cases involve a defendant using a blade as a weapon. These cases bias Courts toward the view that knives are weapons and are bad. When they're presented with an allegedly upstanding citizen carrying a 4" knife, and a police officer who testifies that that 4" knife is primarily designed as a weapon, the logical conclusion is that this is yet another future criminal, and if they don't stop him now, he'll be back in court next year having stabbed someone in a bar-room brawl.
As mentioned above, cases not involving criminal misuse of a knife as a weapon are rare. In most states, there are fewer than a half a dozen cases that really provide valuable information about the legality of knives of particular kinds or lengths, cases that lack any ancillary criminal activity. There are usually even fewer cases -- only a couple -- that are citeable as a controlling authority declaring a knife to be legal; if you're unlucky, there will be no such cases, even for small knives. Cases of either type often hinge on whether the state's testimony would allow a reasonable jury to conclude that the knife in question was prohibited. In most cases, there is no exact description of the knife involved. Often, the length of the knife isn't even mentioned at the (state) Appeals or Supreme Sourt level. When state law doesn't draw any clear line between pocketknives as tools and folding knives as dangerous weapons, unless you get an activist conservative judge who will declare your knife ok as a matter of law, you're at the mercy of the jury -- the trier of fact -- to determine if your knife is a dangerous weapon.
Unless a state's law specifies a blade limit and doesn't leave the door open for illegal weapons less than that length (TX is one of a few that has clear laws, even though its 5.5" limit seems to suggest that legislators were trying to ban knives longer than a certain part of their anatomy), anything other than a SAK might theoretically result in arrest. There are a few states with [state] supreme court decisions which provide a clear length limit, and those limits are fairly safe. Still, nothing can stop supreme court judges from changing their mind, or new supreme court judges from having different views.
