Salve,
One passage of the book relates to perfect passive sentences, but its use in a couple places has left me puzzled:
Dea Discordia…ira mota est.
Here ‘ira’ is ablative. Goddess Discord was moved/affected/roused
with anger? (why not ablative of agent and say “moved by anger”?)
Another:
Quo dono animus iudicis movebitur? With what gift will the judge’s spirit be affected? (again, why not agent and use ‘ab’?)
Gratias
Ablative of agent can only be used with people.
With ideas or inanimate objects, they aren’t actually the agent of the action per se (i.e., there’s no volition), they’re only the means by which or because of which the action happens. Thus, ablative of means/instrument is used instead.
Spiphany,
If I am correct, Wheelock makes no mention of ablative of agent limited to only humans. It would have helped if I knew that in advance. Gratias.
El
I think that in some (rare) circumstances the ablative of agent can be used with inanimate objects when they are being personified (usually ab is used). Personally, I never really saw the benefit to arguing over classifications like this when we all know what ira is doing here.
Elduce,
I just couldn’t believe that Wheelock would have left out such an archetypical item of Latin grammar so I checked the index in my 6th edition.
In Chapter 14, p. 91 I found the Ablative of Means or Instrument, with illustrative examples.
In Chapter 18, p.118 I found the Ablative of Personal Agent, also with many clear examples.
In Chapter 22, p. 142, to round things off, there is a Summary of Ablative Uses, where the Ablative with a Preposition (plenty of examples) is contrasted with the Ablative without a Preposition (including means and manner as well as ‘time when and within which’ and separation).
The sheer clarity of presentation won me over to a book that I had previously thought of as being a it stuffy. Thanks for that. 
Cheers,
Int