The principle of a knife sharpener is very simple. There are different materials that are suitable for sharpening knives. Manual and electric sharpeners function similarly but one is well, you know, electric. The abrasive material on the sharpening slot or sharpening stones must always be harder than the dull blade in question to be ground. If the knife is then treated with a sharpening steel, grindstone, or an electric sharpener, the abrasive material will cause the burr to reposition and align.