I often notice some confusion about netsuke: what is and what is not a netsuke, what they were used for and how, when they were made, and so on.
As a form of art, it is quite straight: they are miniature sculptures (well, at least the katabori netsuke, those sculpted in three dimensions), often made with exquisite craftsmanship, of a large variety of subjects. But do we really know how they were considered in Japan at the time they were made?
Around the mid Edo period, let's say the 18th century, both men and women used to wear the traditional kimono called kosode ("small sleeves" kimono), a robe with no pockets kept together by a large sash, the obi, tied around the waist. But while women used to keep small objects inside the sleeves, men used to carry their personal accessories by hanging them from the sash; such sagemono ("suspended items") comprised money pouches, smoking accessories and inrō to store seals or herbal medicine. Each item would be attached to a double silk cord, about 20 cm long, which would have a netsuke attached at the end: when the sagemono is worn the cord would then be behind the sash and the netsuke would work as a stopper, showing itself from above. For this reason, netsuke always has two holes on the bottom, called himotoshi, where the double cord was inserted. On older netsuke, those really used as explained, we often see one himotoshi larger than the other one: that is because both the cords were inserted through the same hole and then knotted: the large hole would have then accommodated the knot hiding it inside the netsuke itself.
So what about netsuke with small himotoshi or no himotoshi at all (the so-called "natural himotoshi")? How comes they are often of extraordinary quality but look so fragile for a real use? What we find in paintings and prints from the Edo period are almost invariably "round" netsuke, which means manjū or kagamibuta types: these were simple, circular netsukes, carved or with metal applications, very resistant and convenient for use, as they would not catch in the kimono fabric. It is likely that at a certain point, probably around 1820, katabori netsuke started to be collected as works of art rather than functional objects; this would explain also why older pieces often show signs of wear and patina differences in the front and back sides, while later ones look as if they were just made.