Rupert Atkinson wrote:
Jun is right on the mark, except that most schools adopt an either / or approach. They either use irimi & tenkan, or omote & ura, but not both. Jun's description is actually better - more useful.
Also, for myself, I have found it very useful to think of irimi as reversing uke's energy back upon uke, and to think of tenkan as allowing it to continue on, with a little extra added for good measure. I find this helps my Aiki more - thinking of 'movement' rather than 'position'.
Well, in Japanese we have both. Omote/ura are aspects; irimi/tenkan are movements. So a house has an omote-gawa and an ura-gawa: a front and a back. You would never call the front of a house irimi and the back tenkan.
The omote/ura distinction was taken from ordinary Japanese and applied to aikido as a rough classification of aspects. If you start with ordinary Japanese, you can see how the distinction applies--and also how it does not. The mistake is to think of the pair as movements, which they are not.