Whether you're vacillating about tip-up versus tip-down carry or simply feel like reading a vaguely nuanced approach to the underlying theories I hope this is an interesting read.
There are two ways to carry a folding knife clipped to a pocket: tip up and tip down. This refers to the direction the tip of the blade is facing when the knife is stowed away. Another way to think about this is with respect to the pivot screw; if the clip is affixed near the pivot screw the knife carries tip down and, conversely, if the clip is affixed on the opposite side the knife carries tip up.
There are a few different things that should be considered when making the decision to carry tip up or tip down. Among those are comfort, safety, and deployment.
Comfort isn't necessarily the biggest concern when it comes to choosing to carry tip up or tip down, but it's worth mentioning.
Typically, when I refer to comfort I'm thinking about how comfortable something is while it's being carried on one's person (e.g., in a pocket, on a lanyard, or what have you). Here, though, I'm thinking about comfort when the knife is being used.
As I mentioned earlier, tip up or tip down carry places the pocket clip at different points on the handle of the knife. Tip up carry means that the pocket clip will be further down the handle and tip down carry places the clip further toward the blade. This, of course, translates directly to where the clip sits in the hand. In blade-forward grips (i.e., when the pivot is between the thumb and index finger) a knife that's configured for tip up carry places the pocket clip much deeper into the palm of the hand. This can often be more comfortable than the alternative, tip down carry, which places the clip much closer to the top of the grip and, consequently, much closer to where most people tend to apply pressure to the handle.
The size and shape of the pocket clip is a major factor here, too. Intuitively, clips with smaller profiles and smooth edges will be more comfortable than their unshapely brethren.
In the grand scheme of things comfort, as mentioned, isn't very important. Safety and deployment are far more essential to consider.
Both tip up or tip down carry have various safety advantages and disadvantages.
The biggest safety concern when carrying any knife is the blade opening slightly in the pocket. If this were to occur injury could result either when attempting to retrieve the knife (or something else) from the pocket or, perhaps, when sitting or bending the leg forward at the hip. In either of these instances it's possible to be stabbed or sliced by the blade. In case you're wondering, being stabbed isn't good.
Tip down carry eliminates the concern of being stabbed or sliced when retrieving the knife or something else from the pocket. In a tip down configuration a hand, when stuffed into the pocket, would first come in contact with the spine of the blade thereby preventing injury.
However, if the blade opens slightly in tip down carry it's possible to be stabbed by the blade when sitting or bending the leg at the hip. The risk is minimal, it seems, and largely depends on what type of pants the knife is secured in (for example, "traditional" jeans have higher pocket lines and potentially greater risk of leg stabbing while khakis tend to have lower sloped pockets potentially minimizing such a risk).
Conversely, it is argued, with tip up carry the same slight opening becomes far more hazardous as the edge is facing upward. This can only happen if the knife is carried with the handle against the rear seam of the pocket such that the blade can open toward the front of the pocket. There is only one reason to carry a knife in that manner and, chances are, as I'll discuss below, most don't need to and shouldn't choose this option.
What about the alternative configuration of tip-up, you ask? With the blade spine against the rear pocket seam the chances of the knife opening even the slightest bit is nullified. Moreover, it's possible to "close" a slightly open blade by snugging the pocket clip - and the handle as a result - closer to the rear of the pocket thereby forcing closed an unintentionally opened blade.
With respect to being stabbed in the leg by the blade in tip up carry, the chances seem minimized. As the blade is pushed up against the pocket wall the knife, as mentioned, has a far more difficult time opening itself. Also, if the blade were to open it would be closer to the side of the pants leg; this places it away from the primary bend, if you will, that occurs when sitting down or bending forward at extreme angles.
With quality knives these risks are further minimized to the point of non-existence. Most high-quality knives (and, to be honest, practically all knives) have blades that close quite securely and require more than simple agitation to open.
If there's one thing that is infinitely important it's the ability to pull a knife from a pocket and have it ready for use quickly. With most knives that means pulling it from the pocket in a manner which allows immediate access to the opening mechanism (be that a thumb stud, thumb hole, flipper, or other device).
Certainly, most people don't and have no need to truly consider shaving seconds or fractions thereof off the deployment of a knife. I am one of those people; I have no use for a knife where fractions of a second count and if I suddenly were thrust into such a situation knife deployment, I imagine, would be among the least of my worries.
However, for academic purposes, let's consider the deployment methods of folding knives quite seriously.
Undeniably, the deployment of a knife must be dictated primarily by its mechanism.
Traditional folding knives with a thumb stud, thumb hole, flipper, or other manually "flicked" opening device as well as out-the-side (OTS) automatics should be carried, as mentioned, in a manner that facilitates quick access to the opening system. From there, how one carries the knife would largely be dictated by personal choice, or so it would seem. I disagree, slightly, with that assessment and believe that there is a "right way" to carry such knives and I'll discuss my assessment later.
Out-the-front (OTF) automatics, naturally, have to be carried tip-down to facilitate quick deployment of the blade. Tip-up carry would compel the user to awkwardly grab at the opening side of the knife placing the palm of his or her hand directly in front of the blade. Worse, perhaps, the user would have to perform some interesting maneuver to place the switch in a convenient position to fire the knife. Also, as far as I've seen, there aren't any manufacturers that consider the existence of some crazy person interested in carrying their OTF automatic knife tip-up, as evidenced by the conspicuous lack of knives with pocket clips capable of being mounted in that configuration.
Finally, we have so-called "waved" knives. Waved knives are those with a device that is intended to catch or snag on the lip of the pocket during deployment thereby opening the blade without additional motion. As an interesting albeit annoying statutory note, waved knives or any folding knife capable of being drawn from the pocket into a locked position are banned here in MA.
With a waved knife, tip-down carry is immediately out of the question. Tip-down carry would eliminate any possibility of using the wave feature as the device cannot catch on the pocket lip and therefore cannot assist the blade open.
With tip-up carry there are two options: first, with the blade against the back wall of the pocket (I'll call this "blade-rear" for convenience) and second with the handle against the back of the pocket (I'll call this "blade-forward").
The major distinction here is with respect to deployment direction. With blade-rear carry the user must pull the knife up and rearward to utilize the wave feature. This results in a ready stance with the deploying arm and the knife toward the rear of the body, almost concealed from view to those facing the user. The knife slides into a traditional forward grip using this method.
Alternatively, when carried tip-up blade-forward using the wave device compels the user to draw with forward motion. This brings the deploying arm and the knife into a forward position with respect to the body. Also, the knife is most naturally grasped into a reverse grip through this method.
I cannot begin to attest to the various advantages or disadvantages to either grip style or initial deployment stance with respect to utilizing a blade for self-defense. I can imagine there are many nuanced debates in various corners of the internet, many close to reaching critical mass.
I carry my knives tip-up blade-rear thereby placing the spine of the blade firmly against the pocket seam and snugly tucked away.
In terms of comfort, this places the pocket clip further away from the areas of the knife where I usually apply grip pressure (that pressure being applied most typically close to the blade pivot).
Safety-wise, the tip-up blade-rear configuration is bombproof. I have never experienced undesired opening of a blade carried in this manner. As such, I have never been injured as a result of pushing my hand into a pocket with a partially open blade.
Deployment of my knife from tip-up blade-rear places the opening mechanism on all my knives in an excellent position. Moreover, it allows a firm initial grip on the knife when pulling it from the pocket. Tip-down blade-forward carry could achieve almost the same result but I find it results in a far more awkward hand position in deployment which compels far too many minute movements to achieve a good working grip.
In my choice of tip-up blade-rear carry I have focused principally on ease of deployment and comfort. Some contest that tip-up is "more dangerous" but I find that assessment contentious. It seems that tip-up blade-rear carry (the only natural option discounting some strange desire to deploy a waved knife forward into a reverse grip) is the safest possible way to carry a folding knife as it places the spine of the blade firmly against a pocket seam while the handle remains firmly clipped to the pocket. As mentioned above, the blade has effectively zero possibility of opening when carried in this manner.
You Probably Shouldn't:
Cross-draw (i.e., carrying the knife in a pocket opposite to the deployment hand's side). Cross-draw, when it comes to folding knives, seems counter-intuitive. I can't seem to fathom a reason to pocket carry in such an awkward manner. Retrieval in all the pants I own is incredibly uncomfortable and unnatural. Also, cross-drawing a folder once again places opening hardware in undesirable positions. I have to say it again, there simply isn't a good reason to cross-draw a folding knife. Fixed blade knives, on the other hand, are another story for another day.
Carry a knife without a pocket clip. Without a pocket clip the dead horse of accidental self-mutilation contemplated by the tip-up versus tip-down safety debate may actually manifest itself. This, perhaps, warrants a reassessment of carry method to meet individual need. However, I'm of the opinion that carrying a folding knife without a pocket clip is a bit silly. Retrieval is hindered (due to the knife sinking to the bottom of whatever pocket it's in), carry comfort is likely diminished (the knife could orient itself in awkward positions) and, as noted, the safety concerns of tip-up versus tip-down carry are far more likely to occur. For these reasons, it seems that a clipless folding knife is less than ideal.
Carry a folding knife in your back pocket. I used to back pocket carry a folding knife (SOG Flash II) and I can't remember why I did. While it's certainly possible to carry a knife in a back pocket doing so raises some concerns that we've already laid to bed with front pocket tip-up blade-rear carry. First, if we're still interested in keeping the blade spine firmly against a pocket seam we have to flip the clip around. This, as with other strange adjustments mentioned above, places the spine of the blade toward the palm when retrieving the knife and, consequently, forces us to use more steps adjusting our grip when attempting to open the knife; opening hardware isn't close to the thumb and index finger and the blade, from its original palm-facing position, can't swing open. Second, as I noticed while back pocket carrying my Flash II, the clip seems to snag on things more often. Third, back pocket carry seems less comfortable (at least in my assessment); carrying a knife clipped to the front pocket has always been more comfortable as there isn't an inflexible mass of metal clipped to your posterior. Finally, back pocket carry places a knife in a slightly less accessible spot when compared to front pocket carry. Accessibility of gear is a big thing in my book and any undue burdens on retrieval are immediately suspect.
The aforementioned concepts, illustrated using a Spyderco Para-Military2.
Tip-up forward carry. Probably the most dangerous in terms of potential disasters.
In tip-up forward carry the blade is uninhibited and may potentially open, posing a hazard during retrieval or even basic carry.
Tip-down forward carry. Deployment following retrieval is relatively easy, but this type of carry still poses some problems.
Blade deployment is a problem in tip-down forward carry. As seen, the blade may open unhindered and can pose a hazard.
Tip-down rearward carry. A decent solution, but deployment after retrieval is complicated by the opening hardware (here a thumb-hole) facing in the wrong direction.
It's unlikely that the blade would open, as depicted, as the rear seam of the pocket acts as a barrier.
Tip-up rearward carry. By far, the best option. Deployment following retrieval is uninhibited and the potential for the blade to unintentionally open in the pocket is minimized.
As with all blade-rear carry, the potential for unintentional opening is nearly zero; the rear seam of the pocket effectively mitigates the risk.
Carry tip-up blade-rear. You don't have a good reason to do otherwise.