M p.93
Βουλομαι is shown to mean “I desire, I want” - Although it has m/p form, it means the active voice. Now, how would you express “he is wanted for questioning”? Same with “αισθανομαι” (“I perceive”) -how to express “he is perceived to be just”? In other words you would need the passive voice to express the above, but the m/p form means the active voice. 
Thanks to all.
Yes the fact that some middle-form verbs are active in sense can make it difficult (though not always impossible) for them to be used in a passive sense. But don’t get caught up on the English words or simple one-to-one correspondence. “Want” and “perceive” don’t always correspond to βούλομαι and αἰσθάνομαι. Even the active “The police want him for questioning” would not use βούλομαι but some other verb (e.g. ζητοῦσιν). Similarly with “He is perceived to be just." Greek has a lot of verbs and a lot of ways of saying things!
I think in both of those cases you would just an entirely different word. “Wanted for questioning” makes me think of passive forms of ζητέω or διώκω, whereas “he is perceived as x” is exactly what the word δοκέω is for.
OK, thank you.