The difference between Katana and Tachi
The shape of the Katana is basically the same as that of the Tachi. One of the differences between the two is that the Katana and the sheath of the Katana are respectively inserted with a small handle and a cymbal: the small handle is a sword about 6 inches long (about 18 cm), which is rarely used.
In combat, it is generally used to cut things and slash. In the swordsman novels, there are occasionally descriptions of throwing a small handle instead of a sword. In general, a Tachi is longer than a Katana, but it does not rule out that it is longer than a long one.
But there is a clear difference between the Katana and the Tachi! That is the side of the inscription on the sword is not the same. Usually when the sword is used, the sword tip should be outward. At this time, if the blade is up, it is a Katana; if the blade is down, it is Tachi. In actual combat, the Tachi is used by the cavalry immediately; the Katana is used by the infantry. The difference between the placement: in the museum, it is the Katana that is placed upwards and the knife is the Tachi.
There is also a saying, different from the point I mentioned above, that the difference between Taito and Kachi is not determined by the way of use.
According to this theory, in the 14th and 15th centuries, Japanese swords were proud of having strong wrists, so they liked to make long tachi to show their bravery and might. In 1617, Japan enacted a law to limit the length of swords, and many samurai were forced to reduce the length of the sword to meet the norms, so the katana was born. But the authenticity of this statement needs to be discussed. If you have to compromise, you can only say that it may have been affected in this way, but the real decisive difference should still be the way of use. After all, it is derived from the weapon industry and different battlefields. It is normal to produce different weapons.