Aikido techniques are frequently referred to as waza 技 (which is Japanese for technique, art or skill). Aikido training is based primarily on two partners practicing pre-arranged forms (kata) rather than freestyle practice. The basic pattern is for the receiver of the technique (uke) to initiate an attack against the person who applies the technique—the 取り tori, or shite 仕手, (depending on aikido style) also referred to as (投げ nage (when applying a throwing technique), who neutralises this attack with an aikido technique.[1]
Both halves of the technique, that of uke and that of tori, are considered essential to aikido training.[1] Both are studying aikido principles of blending and adaptation. Tori learns to blend with and control attacking energy, while uke learns to become calm and flexible in the disadvantageous, off-balance positions in which tori places him. This "receiving" of the technique is called ukemi.[1] Uke continuously seeks to regain balance and cover vulnerabilities (e.g., an exposed side), while tori uses position and timing to keep uke off-balance and vulnerable. In more advanced training, uke may apply reversal techniques (返し技, kaeshi-waza) to regain balance and pin or throw tori.
Ukemi (受身) refers to the act of receiving a technique. Good ukemi involves attention to the technique, the partner and the immediate environment - it is an active rather than a passive "receiving" of Aikido. The fall itself is part of Aikido, and is a way for the practitioner to receive, safely, what would otherwise be a devastating strike or throw (or joint lock control) and return to a standing position in one fluid movement. The person throwing (or applying other technique) must take into account the ukemi ability of his partner, as well as the physical space: walls, weapons (wooden tantō, bokken, jō) on the tatami, and the aikido practitioners nearby.
Uke must attack with a strength and speed appropriate to the skill level of the tori; in the case of beginners, this means an attack of far less severity than would be encountered in a real-life self-defense situation.