The title might make a decent band name, but no, I’m not starting a band. It’s meant to capture the common photo of an instructor grasping either their favored weapon or multiple arms.  Normally they’re clad in the jacket or gambeson that accompanies those tools best. Fancier shots have black backgrounds highlighting vaguely period expressions with a tinge of hipster coolness. Not knocking them, they can be nice, but it’s beyond whatever emotional depth or panache they’re meant to express which I wish to touch on here.
Many if not most fencers in the Olympic orbit become single-weapon fencers. It’s often true in historical circles too. They specialize. Historically, one started out in foil and then perhaps explored sabre or epee. The “three-weapon” fencer actually deserving of the name was, when I was starting out and even when competing, something of a special case. For context, I mean NCAA and USFA fencers between say 18 and 25. Many might dabble in the other weapons, but the fencer who could actually fence each as intended was less common. In my college club there was one fencer who was truly a three-weapon fencer, Dennis.
A close friend, and now one of my oldest, Dennis has more than once been a mentor to me. He will always be. When I was struggling with something new in sabre, for example, he would drill with me until I got it. When I destroyed my right arm in an auto accident, it was Dennis who agreed to train me as a lefty. Even now, Dennis has helped me as he could with an epee coaching class, playing the advanced student for me in video homework. A number of years ago when I was still working on competitive issues in Olympic fencing it was Dennis who ended up co-authoring a paper on difficulties in judging foil. He is versatile. He can help with all these things, and more, because of it.
Beyond the obvious perks to versatility, there is a still more important reason that it’s a goal worth pursuing: depth of understanding. It’s an analogy I’ve used a lot, but studying a different weapon or tradition is like learning a new language, one that helps you understand your own that much better. Over the past year, when most of us have been unable to meet up to fence, I’ve watched and/or advised people working in isolation. Some had partners to train with, many more did not. But what I noticed in each case was the more that these students included disciplines and weapons they didn’t normally study the better they got at their primary focus. More than that, their understanding of the universal principles underlaying all fencing increased. It was akin to watching what I imagine Dennis’ first few years fencing were like.
It can be daunting trying something new. At a certain point in training, however, it can be the catalyst one requires for growth. This raises an important question—when should one start dabbling in other weapons and forms? Alex Spreier (High Desert Armizare, Bend, OR), in a short thought-piece I shared here a while back (“Alex Spreier on Universals,” 2 May 2021), summed it up well:
The first step on the road to being able to discern patterns, principles, and universal aspects of the Art is the one I expect will be the most controversial – you need to spend 3 to 5 years focusing on developing your skills within one system. This allows you to build up a “vocabulary” of how to move your body, how to respond to threats, how to create threats, and ultimately this vocabulary will enable you to start recognizing patterns. And recognizing patterns is key to uncovering principles.
The idea of dedicated, formal study of one system or weapon for years goes against common practice in “HEMA,” but it is nonetheless the best path to improvement. As Alex explains, what this focused time does is impart the necessary skills to acquire new ones later; at the same time, it builds an intellectual framework and vocabulary that assists pattern recognition and retention in learning.
On an app that serves as the virtual lounge for the “collective” of schools that work together in this part of the PNW, we have had several ongoing discussions; in depth, evidence-driven conversations about key principles, ideas, or techniques that we have less information for than we’d like. One in particular highlights the importance of cross-training and text-diving.
Ex. Mezzo Tempo & Counter-time
The example in question was put forth by one of the instructors, Andy Playmate (Northwest Armizare), who has been running the longsword pod. In looking at tempo in longsword, and what a few different interpretations/translations say, he asked about Vadi’s notion of mezzo tempo or half-tempo and how it relates to counter time, attacks in preparation, etc. A rapier fencer as well, he asked questions related to both weapons: “what do you think the relationship is between mezzo tempo and stop cut/thrust? And second, did stop cut evolve from Mezzo tempo or somewhere else?” Great questions and ones which underscore how difficult it can be to unravel key concepts even armed with good training and vocabulary.
Starting with Philippo Vadi (fl. 1480), what does he say?
I do not have a copy of Vadi handy, so here I will rely on Guy Windsor’s translation available at Wiktenauer:
Chapter XIIII. Theory of the half tempo of the sword
I cannot show you in writing
The theory and way of the half tempo
Because the shortness of the tempo and its strike
Reside in the wrist. 
The half tempo is just one turn
Of the wrist: quick and immediately striking,
It can rarely fail
When it is done in good measure.
If you note well my text,
One who does not practice [the art] will get into trouble:
Often the quick flight from one side to another
Breaks with a good edge the other’s brain.
Of all the art this is the jewel,
Because in one go it strikes and parries.
Oh what a valuable thing, To practice it according to the good principles,
It will let you carry the banner of the Art. 
In my reading of Vadi, mezzo-tempo here suggests an action that blocks and cuts/thrusts at the same time. For once, Florio’s glossary [http://www.pbm.com/~lindahl/florio/] may be helpful here. He defines mezzo a few ways, but while it can mean “half,” it can also mean “a mediator, or intercessor. As a space or interveall of time or place” (313). Mezzo here may mean more “middle” as an action that either splits the difference or occurs during the “middle” of an opponent’s attack; mid-tempo. I can’t say that for sure, but given what Vadi says here—and going by Windsor’s translation—that makes sense to me. One way to illustrate this is to image that Fencer A throws a cut, a mandritto fendente, and B selects the time in which that cut is still developing to intercept it with a cut of their own, likely with a step somewhat to the side (to the right assuming two right-handers) that at once blocks and stops the incoming attack and that strikes at the same time. A close out like this, something later rapier masters saw as ideal, might be defined as a type of counter-attack, but perhaps the most accurate term would be an attack into preparation or an attack into tempo, that is, where one attacks as the opponent initiates their attack. Certainly what Vadi describes here is in line with later masters. 
Looking at what other masters say about mezzo tempo makes sense as we try to figure out Vadi. For Italy, the next generation of masters, especially the Bolognese school, is a logical next step. The Bolognese masters also employ the term, but don’t agree amongst themselves as to definition. The Anonimo and Viggiani, to name two, both use mezzo tempo but define it slightly differently. Viggiani, for example, wrote:
Sometimes one attacks with a half blow, in mezzo tempo. It is true that the majority of attacking is in mezzo tempo, since, when there are two who are well schooled in the art, he who wishes to attack will deceive his companion in such a fashion that, when his adversary is about to perform a blow, he enters with dexterity and speed and strikes in the middle of the adversary’s blow with a half blow
In the Anonimo, mezzo tempo is an attack into preparation, and contra tempo is what we see in Vadi, an attack into tempo that closes out the opposing steel and strikes simultaneously. The author of the Anonimo uses more ink to explain that there is no such thing as a half tempo, but that since one can make a “half attack,” that is, one that stops at stretto distance and is made more quickly, that they refer to it as “half” tempo (as an aside, this is a lovely example of a fencing text differentiating tempo and speed). Again, “mid-tempo” might be a better translation. Regardless, the Anonimo offers less detail about mezzo tempo. As to counter time, we read “Contratempo happens when the enemy wishes to strike, and you interrupt his attack, rendering it useless, while you simultaneously make one that strikes him.”
Dal’Aggochie, as Mike Cherba pointed out, was probably the clearest. For him, mezzo tempo is “A half tempo, the final one,… when you attack while the enemy is throwing his blow.” 
Um, they don’t Agree, so… what now?
So, what is the student to do with all this? How does one reconcile these disparate definitions? Vadi, Viggiani, the Anonimo, and Dal’Aggochie all include mezzo tempo, but don’t agree. It can help to group them together and see how they differ. All include an attack that interrupts that of the opponent. Vadi and Viggiani call this mezzo tempo; the Anonimo calls the same thing contra tempo. Dal’Aggochie may refer to the same thing; his half tempo sounds much the same as the others, but being less specific as to when exactly one attacks the enemy it’s less clear. Is the attack made as they are preparing (an attack in prep), as they are mid-strike (half-tempo), or is it in response to a counter attack (contra tempo)?
This is where looking at the modern definition, one derived from this tradition, can be helpful. It may not be the same, that is always a possibility, but it’s a place to start. Counter-time, sometimes referred to as contretemps (Fr.) or contra-tempo (It.), is different from the early notion of mezzo tempo. It’s usually a technique for more advanced fencers. Not each master in the past defined it quite the same way, though most tend to suggest the definition that survives today, that is, “a planned action made against an opponent’s stop-thrust or stop-cut. First draw out the stop hit, and then parry it and hit the opponent in a lunge.”  Other definitions are similar.
Here is one from the wiki at Academie Duello, Vancouver, Canada: “this is the opportunity to strike during an opponent’s offensive action with a shorter attack of your own that closes the line.” 
Masaniello Parise (1884), discussing counter time for sabre, not surprisingly is more in line with current definitions. This action is made “with veracity, advancing a step and immediately defending with a circular or opposition parry against the opponent’s action in tempo [i.e. counter-attack], and secure in defense, and ripostes without delay.” 
There are, however, exceptions. On one page of an old site at the University of Northern Arizona, guessing one of William Wilson’s, the editor quotes the Pallas Armata (1639) and defines contratempo as “a thrust in the same line that your adversary thrusts in (Pallas Armata, p. 6).” 
With the exception of this last definition, all describe a counter-offensive action made against someone making a counter-attack. It’s not specific to weapon, only the tempo in which a weapon, any hand-to-hand weapon, might be used. The distance required by such a maneuver is critical as is the speed and accuracy with which one strikes. Tempo, distance, speed, judgment, initiative, these are all universals, the elements underpinning all fencing.
Returning to Andy’s question, “what do you think the relationship is between mezzo tempo and stop cut/thrust? And second, did stop cut evolve from Mezzo tempo or somewhere else?” what can we say after reviewing some of the literature?
My answer would be that a stop thrust, if it closes the line as it lands, might be an example of mezzo tempo. Certainly that seems to fit the majority of the definitions we just examined. A stop cut might too, but these often do not close out the line—they are cuts made against an open line, but always followed by a parry and riposte in case the stop cut fails. Since it’s not usually the final blow, a stop cut doesn’t fit Dal’Aggochie’s definition well either; it’s a counter-attack followed by a defensive action. Stop-cuts, like stop-thrusts, are attacks of opportunity, but less likely performed with a close out. I’ve not touched the second question, but attacks against the forward target are reflected in more than one medieval source—for a graphic example the hands lopped off and flying in Talhoffer (ca. 1467) might serve. While the stop cut we use in sabre may derive from something native to cutting weapons, it’s not impossible that the later stop-hit/stop-thrust derived from the rapier iteration of mezzo-tempo. I’m not sure what work has been done on this if any, but it might be fun to explore.
What I’ve hoped to show with this example is two-fold. First, time spent (at the appropriate stage) working on additional weapons or systems increases our understanding. The fencers asking these questions arrived at them thanks to cross-training. They’re making connections, seeing parallels as well as key differences.
Second, the increase in awareness and understanding, in seeing yet again how the same universal principles apply, makes it that much easier to “unpack” the next new system or weapon. This doesn’t mean that it is easy, just easier. In the aggregate our knowledge and skill should grow and improve.
Importantly, one must be cautious not to misapply modern understanding, or worse—exceptions, onto the past. The more one knows of the universals across time, across masters and texts and periods, the less likely this is a danger. Many members of the historical community make the mistake of assuming anyone referencing modern works is, by definition, guilty of anachronism. That is not true, but it can look that way to someone unarmed with that knowledge and understanding. Since they cannot distinguish between excesses that help one gain points in a sport, and the universal principles that most fencers learn before they try on the silly stuff, they have trouble seeing how anything past 1500 can have any relevance. Modern discussion of the universal principles did not pop out of a cereal box on the 1 of January, 1900 or 2000; they derive from the corpus of works we read in historical fencing. Time spent with solid modern works, like time spent with another weapon, so long as approached responsibly, will help more than hinder.
 A quick google search using the terms “fencing instructor portrait” will bring up some decent examples.
 “Wrist” here makes more sense than “knot,” though polso is the modern Italian for “wrist.” Nodo, here, can mean knot, but it can mean junction, crux, etc., and my guess is that the other translators may have used Florio’s 1611 Dictionary (p. 333; cf. http://www.pbm.com/~lindahl/florio/), where he stipulates that Nódo can mean “also the joint of any cane.” By context Vadi clearly means turning the hands so that one simultaneously blocks and strikes. “Of all the art this is the jewel” certainly makes sense in light of that idea.
 For Vadi, https://www.wiktenauer.com/wiki/Philippo_di_Vadi#Introduction
 Cf. Marcelli, Rules of Fencing (1686), I.I. Ch. IV., 23 in Holzman’s translation.
 For Viggiani, see W. Jherek Swanger, The Fencing Method of Angelo Viggiani: Lo Schermo, 64r; p. 7 of the pdf; for The Anonimo, see Stephen Fratus, trans., With Malice and Cunning: Anonymous 16th Century Manuscript on Bolognese Swordsmanship, Lulu Press, 2020, 64 (see also p. 49); for Dal’Aggochie, see The Art of Defense: On Fencing, the Joust, and Battle Formation, trans. Jherek Swanger, Lulu Press, 2018, 29v.
 Rob Handelman, and Connie Louie, Fencing Foil: A Practical Training Guide for Coaches, Parents and Young Athletes (San Francisco, CA: Pattinando Publishing, 2014),441.
 See Christopher A. Holzman, ed., The Roman-Neapolitan School of Fencing: The Collected Works of Masaniello Parise, Wichita, KS: Lulu Press, 2015, 272-273.