Here's something that's been on my mind for a while. Sometimes there is no distinction either in form or meaning between a perfective passive participle and an adjective. Take the following as an example from Orberg's LLPSI Cap XXXIX:
"O fortunati, quorum iam moenia surgunt!"
ait Aeneas alta urbis tecta suspiciens, ac nebula cinctus (mirabile dictu!) in urbem penetrat per medios homines ambulans neque ab ullo cernitur.
Now cinctus here could be simply the masc. nom. sing. of the adjective: cinctus, -a, -um or it could be the per. pass. part. of cingo, cingere, cinxi, cinctum - as in he is surrounded by fog. But there is no difference in meaning or form. Is there a grammatical difference within the sentence between the two?