Tachi is a Japanese sword, more curved and slightly longer than the katana. It is worn with cutting-edge down and is sually used by cavalry. The katana is the Japanese long sword (Daito), Many Japanese use this word, katana, generically as a catch all word for sword. Tachi is the word used on the USAF test forms for sword. In Aikido a boken or wooden sword is used. When treated as a carry sword it is carried edge up so it is considered a katana. Therefore in this context tachi is used to mean a katana or more practically, a boken.
In Aikido we are not trying to become swordsmen. The sword is used to help us understand the Aikido movements and as part of the tradition. Aikidoka who aspire to be swordsmen frequently take Iaido to learn sword handling.
|Gripping the sword is very important. The section on Grasping Reflex explains important details. Here note that:
|Fig. 1 Sword Grip|