Originally Posted by Rat
That is a very good illustration; but it shows two ropes joined at the end.
It shows a Bowline straight from Grog's page with a small section photo shopped out for demonstration purposes. If you imagine the lower loop stretched out ( and in a different diameter) It is a sheetbend.
As I said, you could never practically tie a bowline using the same movements and mechanics as the sheet bend because normally if you're tying a bowling the standing end is fixed already or is 100' long and ( And who wants to feed all that through a knot?)
When I teach I teach a bowline as a knot used to put a non-constricting fixed loop in a single piece of rope. And I always teach it with a backup. ( or more commonly I teach a figure 8 because it maintains more strength and doesn't need a backup, although it will be a bear to untie when weighted. but if I'm teaching a rescue scenario, I'm much more concerned with the right now. I'll cut the rope later. )
When I teach a Sheet bend I teach it as a superior method of joining two ropes together , over the Square knot, especially in slippery ropes, small diameter cordage and ropes of different diameters.
But the fact remains if you tie both properly and cut free all four ends to leave just a lump with four fuzzy ends, the actual knot that will be left behind is identical.