I have dabbled with the application of the knife as a defensive tool over the years and it has remained the red-headed stepchild of defensive tools for myself. Now, to be clear, it is a foremost preparedness tool in that having a cutting tool on person is essential; having a rescue-cutting implement to free people from stuck seatbelts or other snares is important. However, the knife’s role in defensive application remains ephemeral for myself. A folding knife or a multi tool with a blade can serve the role of rescue tool, but a fixed blade knife is the best solution for those who consider the knife an important part of their defensive toolset.
An edged weapon causes hemorrhaging through slashing or stabbing wounds and this is how it inflicts damage and possible lethality. The edged weapon is utterly lethal and the judicial system views the knife the same as it views the gun in treating it as a lethal weapon only. If a knife comes into play in self-defense it can only be justified if the application of lethal force is justified. The knife does not inhabit some lower tier of force than does the firearm, though it seems many people think that is the case.
The issue I take with the edged weapon as a defensive tool is the fact that, although it is entirely lethal in the eyes of the law, it is far less decisive in ending fights than is the firearm, generally. Yes, it is exceedingly lethal because it has the ability to sever major blood vessels and cause deadly bleeding, but the mechanism by which it forces a physical stop is exceedingly unreliable. Many people who have been stabbed in the course of a fight thought that they were just getting punched in the moment. Granted, determined adversaries can fight through all but a nervous system hit with gunfire, but the weapon at least provides the means of a rapid termination if the shot can be made.
In my opinion, based on the research I have done and the training that I have done, the most practical application of the knife in defensive use is as a “get off me” tool that is best used by stabbing at the ocular cavity and the neck area of an opponent. The reason I make this claim is that striking those vital areas of a human being usually elicits a reaction that drives the opponent to break contact. Even the most determined and crazy individual usually can’t ignore a sharp implement being forced into their ocular cavity. Stabbing the face or neck is, quite obviously, absolutely lethal in nature, but I remind the reader that there is no in-between mode with an edged weapon. Like a gun, the weapon is only going to be justified in use if a lethal response is justified. Therefore, no matter how brutal it appears, stabbing the ocular cavity and neck area will most likely register with the threat to change their behavior.
I submit that carrying a blade when one cannot carry a gun (though the legalities of restricted locations often prohibit both) is sound as it gives you a lethal force tool that is inferior, but lethal, none-the-less. The notion of carrying an edged weapon instead of a firearm, however, is ridiculous if you have the choice to carry a gun. carrying a blade that is accessible to your support hand to give you a contact distance weapon that can be used to help retain your gun or make space so that you can access your gun is where I believe the edged weapon serves its most practical purpose for the armed citizen. This, however, is indeed a niche consideration.
We must consider the optics of edged weapon use; rationality should determine that lethal force is either justified, or not, and the weapon used should be irrelevant. There have been plenty of edged weapon defensive uses that have been deemed legitimate self-defense and have not been prosecuted, that is true. However, we can also find examples where the use of a blade puts the self-defender under increased scrutiny. The public and the justice system tend to view the use of edged weapons as felonious, and this is an unfortunate, yet real, consideration. The firearm not only proves the far more effective defensive tool, but it remains the more acceptable tool to be used.
If an armed citizen carries a blade when unable to carry a gun, or accessible to the support hand even when carrying a gun to foster weapon retention, I can hardly take issue. However, I find that many people consider the blade a magic talisman of sorts and don’t realize how limited the defensive application of the tool actually is. In closing, I would submit that the knife proves viable only if you have the fighting skills to effectively employ it. Can you effectively strike? Can you grapple? If not, I think that you are fooling yourself if you think the knife will greatly enhance your abilities. Yes, there is the deterrence factor that is always possible, as displaying a knife might make an attacker quickly change his mind, but relying in only this is not sound.
To effectively use a blade you need to have the overall hand skills to do so, and if you have those skills then other tools become quite viable in contact distance defense as well. Impact tools such as saps and jacks (unfortunately, very illegal in most jurisdictions) may well serve more formidable than edged weapons in actually ending fights quickly as impact registers immediately whereas bleeding out often does not. Even flashlights and pocket sticks can be used quite effectively for impact in the hands of a trained individual and such implements are much easier justified after the fact. The legal pitfalls of using a blade for defensive purposes should be cautiously considered and the limitations of the tool should be acknowledged.
My two cents.