Line of Attack
The "line of attack" refers to the line connecting the attack and the target. Aikido techniques avoid the direct energy of an attack instead of stopping that energy. It is the difference between dodging a punch and blocking a punch. Fundamental techniques emphasize moving off the line of attack to apply the defense.
Blending with an attack means to unite with the energy of the attack instead of clashing with it. It is like two rivers merging together into one single flow. Uniting with the energy of the attack allows us to take control and redirect that energy to an appropriate resolution.
Taking the Balance
An object is stable when its center of gravity is over its base of support. Aikido techniques disrupt the attacker's stability by moving their center of gravity so that it is no longer over their base of support. We call this "taking the balance" of the attacker. This is accomplished with a combination of drawing out the attacker's center, raising the attacker's center of gravity, reducing the attacker's base of support, and restricting the attacker's ability to regain balance. An attacker can be thrown or restrained without using much strength once their balance is compromised.