Answer: The difference between the two is that one removes material and the other does not.
Sharpening a knife will remove material from the knife. This creates a new cutting edge. Honing a knife will straighten material that's already on the cutting edge of a knife.
Why does this matter?
Honing is a great practice for extending the sharpness of a cutting blade edge between sharpening services. Microscopically, the honing process will realign the "folded" micro parts of a knife's cutting edge that occur each time it's used thus making it sharper. This can be done numerous times. However, it's also possible to round out a knife with a hone. In this case a new edge is required to bring back a cutting (vs tearing) action to your knives.
We've heard of chefs getting their knives sharpened every day on the extreme and every week on the slightly less extreme. Further, we've heard of chef's recommending the home cook sharpen 1-4 times a year depending on usage. Extend your sharp edges by honing during the months in between sharpenings.
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