Quote Originally Posted by ranagrande View Post
That is a reasonable interpretation, but it's not RAW. The spell makes no mention of intended wielder, only the wielder. The spell quotes a general rule about weapon categories, but is doing so for the new purpose of determining the sizes of animated objects. The rules cover different things and must be considered independently. Perhaps the omission of the line about the intended wielder was intentional? Perhaps the similarity between the rules in coincidental? It doesn't matter for RAW in this case. Specific trumps general, and the spell effect requires a wielder.
Perhaps we should make a new thread to discuss this. If you disagree with what I say next, then start a new thread and I will follow.

First, spell descriptions repeat general rules all the time.
Quote Originally Posted by Tortoise Shell
The enhancement bonus provided by tortoise shell stacks with the target's natural armor bonus, but not with other enhancement bonuses to natural armor.
Quote Originally Posted by Toughen Construct
The enhancement bonus provided by toughen construct stacks with the target's natural armor bonus, but not with other enhancement bonuses to natural armor.
To claim the literal copy and paste of the general rule for weapon size categories is a separate new rule and everything is just a coincidence is quite the stretch.

Second, lets take your logic step by step.
1. The spell targets any weapon.
2. The spell does nothing on weapons held or carried by other creatures.
3. If the targeted weapon is not held or carried by other creatures it becomes animate
4. The animated weapon's size category is determined by its relation with its "wielder" and not its actual object size.

You're saying if the wizard targets a sword lying on the ground, the spell will do nothing because it does not have instructions on what happens when you target an unwielded weapon.

But this is incorrect because there are instructions. The unwielded weapon becomes animate. You just don't know what size category it will be treated as. So one could say whether the Colossal Weapon is treated as a Colossal, Gargantuan, or Huge object is DM's discretion.

To repeat, if we follow your line of reasoning, whether the weapon becomes animate or not is not up to DM discretion. Only its size category is. The weapon will become animate. Unattended weapons are not a failstate of the spell.

But this is also incorrect. Because if the specific rules don't cover the scenario at hand, we default to the general rules, which once again say the colossal weapon will be colossal sized.