|Extant jian probably dated to Ming period.|
In this blog post, I will share some of my thoughts on this issue in Chinese context. Do note that these are all speculations, as the reasons behind the design of a particular weapon can't be proven.
1. Chinese swords were used together with shields
|Section of the scroll painting 'Wakō-zukan (《倭寇図巻》)' depicting Ming swordsmen armed with large shields. All but one of them are wielding jian.|
2. Prevalence of archery, particularly horseback archery.
|Section of the Ming period scroll painting 'Shang Lin Tu (《上林圖》)' by famous Ming painter Qiu Ying (仇英), depicting a hunt scene.|
Turkish archer demonstrating one of the methods of shooting a bow with a sabre in hand. This is also one of the advantages of thumb draw ("Mongolian draw") compared to two or three-finger draw ("Flemish draw" or "Mediterranean draw").
Horse archers, particularly medium cavalry that often had to engage in close combat, were required to be able to switch weapon in quick order. Some horse archers (particularly the Turks) were known to shoot their bows with a sword readied in their right hands. A sword with complex hilt is uncomfortable to wear (especially when worn together with bow bag and quiver), harder to draw quickly and gets in the way of archery movements.
3. Religious root
|Ming period painting of Lu Dong Bing (呂洞賓), one of the five patriarchs of Daoist religion, with a jian hung on his back. Currently kept at Philadelphia Museum of Art.|
|The two-finger gesture known as Jian Zhi (劍指, lit. 'Sword finger') is a common sight in Chinese swordsmanship but serves no practical purpose. It is actually a modified Daoist hand seal.|
4. Tip cutting and tip parrying
“The length of a sword is three chi, but only the edge of the first cun is (regularly) used.”
— Chinese martial arts saying
Generally speaking, a Chinese jian has very little distal and profile tapering comparing to its European counterparts, and has a point of balance farther from its guard. It can be utilised for Dian Jian (點劍, lit. 'Point sword', cutting with the tip) attack, a technique that is rarely seen in other swordsmanship systems. Chinese jian (and many Eastern swords) can also use its foible to defend and parry as well as cut through an opponent's cut. Whether ancient swordsmen designed their techniques around the weapon, or the weapon evolved over time to accommodate the techniques, is up for debate.
|Section of a Yuan period mural in the Sanqing Hall of Yongle Palace, depicting a religious figure holding a jian with a unusually long crossguard. He is also using the so-called "rapier grip".|