.Same for throwing a spear and using the spear skill, (or throwing an axe and using the axes skill, like I put forward).It's still incredibly counter-intuitive to place a Throwing Knife in the Swords group as they are not remotely used in the same manner. Training in swordmanship has absolutely no bearing on how one would use a Throwing Knife.
No, it is not the same. Spears (at least many shorter spears) are meant to be thrown, as are some axes. I would, for example, class Javelins as Short Spears and treat them as such. Swords are simply not meant or designed to be thrown; it is not part of that skill set.
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.Yes it is counter-intuitive I agree, but working within the confines of what is already in the book it seems the best solution. Not the most elegant I agree, but factoring in all the mechanical and feel good feeling at the table, it seems the best option. Of course it is all house rule anyway. In the end I can't see throwing knives being taken too often anyway, it was more for symmetry that I included it.
It is one solution. Or, we could rule that an Exotic Martial Weapon (Throwing Knife, Sling, etc.) is treated as though it is its own Combat proficiency (initial ranking determined using the Brawling rules) and it can only be improved during a Fellowship phase by using Adventure points to buy new ranks. A Loremaster might further rule that a Hero must find a teacher who is already proficient with the exotic weapon to obtain the full benefits of using that weapon. Might this be a better solution?