Darnitt, you're already on the second page, Kentucky! No one answered! I'll give it a shot. This may not be right, so take that in mind. I "think" it can be either or. As in it is not improper to have the "left" side flat and not concave. I don't know the term for the left side of the blade, Stacy does! But it can be either or. The reason for the concavity in deba knives and yanagibas and what have you is ease of sharpening. The left side must be flat, and the concave feature makes it much easier, as there is much less material to remove when trying to make it dead flat. Hope that helps.