The "past participle" occurs as one of the two parts of the perfect/completive aspect, here in active voice:My fault for being confusing about terminology. When I said that the "past participle" should be called the "passive participle," I was referring just to "past" participles that modify nouns (in participial phrases), not to the entire class of inflected verbs that end in -ed (for regular verbs) and -en (for most irregular verbs). Verb forms in this class have several functions: they can follow forms of the perfect have (She has/had eaten) and they can follow forms of the passive be (The cookie is/was/has been/had been eaten). My claim is that so-called "past" participles that modify nouns belong to the later category and, consequently, "passive participle" is an appropriate designation for them.ACTIVE: The child has eaten the cookie.
Passive: The cookie has been eaten by the child.Thus, the past participle occurs in active voice and passive voice.
Johanna Rubba rightly points out that some noun-modifying "past participles" are not passive: the fallen tree, the retired teacher, the expired subscription. These are relatively infrequent; I'd speculate that in any random corpus, 95% of the noun-modifying "past" participles would be passive. Although not grammatically passive, semantically they describe an act that has happened to the noun, not something the noun does. It is significant that they can be preceded by be as well as have (The tree is fallen, The teacher is retired, The subscription is expired), and I'd contend that these are the source of the noun-modifiers, not the perfect forms (The tree has fallen, etc.). Syntax is rule-governed and loves generalizations, and there are no generalizations involving a connection between the perfect and the noun-modifying "past" participle. Very few perfects could be said to have corresponding noun-modifying past participles. For example, "the forgotten man" always relates to "the man who is forgotten," never to "the man who has forgotten."
Dick Veit