There are three main principles in Aikido that you're going to come across a lot in the Dojo. That's to blend, extend, and to lead your partner. Aikido literally translates to the way of harmonizing energy. That's not just a pretty name. That really comes across in how we interact with each other and how we practice the martial art in general.
In order to think about blending, extending, and leading let's take a look here. We're going to start with Gyaku Hanmi Katate Dori, wrist grab. Again, the idea of blending is that I don't want to fight directly along my partner's line of strength. If he's grabbing here my first reaction is generally to either push or to pull away from that. I don't want to fight directly with his line. So, what I'm going to do is, as his energy is coming in this direction, I'm going to blend and allow it to continue in that direction so I don't end up fighting with it. As he's coming in this direction, Tenkan, move out of the way of the line of his attack, and I should be able to put myself in a safer position. Again, as his energy is coming down this direction, step off the line of attack, and let the energy continue to move. I should be in a better position.
Blending is also considered a way of leading my partner. I don't want to get in this position and pull. I don't want to contract. If we get in this position, extend to lead my partner around. Blend, lead. Another way we can see this is in Morote Dori, a two handed grab. In order, again, to not fight directly with his power I want to find a way to point my extension in the direction he's going. I can use that same body movement to extend, blend, and lead my partner around. I cannot do this if I collapse. So, blend in the direction of his power, extend to keep that shape, and lead your partner.
Blend, extend, and lead.