“This is a verb that is middle or passive in form but active in meaning. Its form is always middle or passive, but its meaning is always active. It can never have a passive meaning.”
However, it seems like a better much definition for deponent verbs would be closer to the one given by Stephen Carlson, a Greek instructor and member of the graduate program at Duke University who wrote the following in a recent post to the B-Greek forums,
“Classifying something as ‘deponent’ isn’t really helpful. It just means a middle-morphology verb whose active form is so rare or missing that you have to look it up under its middle form in the lexicon.”
So deponency is really a lexical issue rather than a formal issue. There is nothing in a deponent verb’s form that requires it to be labeled as such, other than a lack of a common active form. Instead, it is the verb’s lexical meaning that determines where it sits on the spectrum of how active, middle/reflexive or passive. Certain verbs were likely so intrinsically middle or reflexive that an active form was much less useful in common writing and speaking, which eventually resulted in the active form dropping out of use (and therefore being dropped from our lexicons – hence deponent!)
It seems like this should be taught from the beginning. In Attic intro textbooks are deponent verbs presented in this way?