Why can’t words like interested and other similar past participles, which are adjectives, be placed before their noun?
I was taught an adjective can be placed before noun to describe it. When asked, my teacher does not seem to give me a clear explanation why I cannot put an adjective like interested before noun.
You can put interested before a noun (e.g., The interested reader can find more detail below.) In general, in English, you can put past participles before nouns (e.g., the completed picture).
Perhaps you could give an example that your instructor has criticized, because several counterexamples occur to me. "The lawyers failed to send notices to all interested persons." "Some of the children were not interested, and those bored children might have ruined the class for the rest."
UPDATED PER CLARIFICATION FROM OP
My teacher just showed me the definition of the word in the dictionary (Longman Dictionary of Contemporary English). Indeed, there are many other past participle adjectives e.g., riveted, intriqued, spellbound etc, that, according to the dictionary, cannot or are not supposed to be placed before noun. – Kwanbhan
I think your teacher is either misreading or misapplying Longman. The dictionary itself pre-positions adjectival participles in its examples, e.g.,
car‧bon‧at‧ed . . . carbonated drinks contain small bubbles [↪ fizzy]: carbonated spring water
http://www.ldoceonline.com/dictionary/carbonated
in‧terest‧ed [sic] . . . 3 interested party/group a person or group that is directly or personally concerned with a situation and is likely to be affected by its results [≠ disinterested]: All interested parties are invited to attend the meeting.
http://www.ldoceonline.com/dictionary/interested
But see
riv‧et . . . 1 be riveted on/to/by something if your attention is riveted on something, you are so interested or so frightened that you keep looking at it: All eyes were riveted on her in horror.
http://www.ldoceonline.com/dictionary/rivet_1
It could be that the contraposition of examples like the first two against the has suggested to the teacher that a participle cannot be pre-positioned unless an example is provided, but any first-year philosophy student can see the inductive fallacy there.
It may, as commenter @FumbleFingers suggests, that some words like "knelt" do not admit of this usage, but I am hard-pressed to imagine, much less to find, a rule that sorts one category from the other. The same commenter suggests "dreamt" can't be used this way, but this teacher's dreamt-up proscription belies in existence what it denies in substance. "Had" and "been" are also suggested, but I don't see why a person couldn't think of a raucous party and remember the good times had, the drinks drunk, and the debaucheries unspoken. If those participles can be post-positioned, then why not pre-positioned _in the appropriate instance of their use?
In sum, I tend to think it's more a matter of taste and style to be evaluated in each individual usage, rather than a matter of grammar or syntax.
If I remember correctly, and it is possible I don't, it is frowned upon to use verb forms as adjectives before nouns because of confusion with helping verbs. In FumbleFingers' example “this jacket has reinforced riveted seams”, the verb have (or has in this case) modifies the verb reinforce (reinforced) thereby changing the sentence's meaning. Because of this modification, the example could be interpreted as meaning that the jacket itself reinforced the riveted seams. Hence the general rule. However it should be noted that this could be avoided by using proper punctuation, such as a comma separating the two descriptives.
The adjectives alone-asleep-ashamed-awake-afloat-afraid-alight-alike-alive (there may be others) are not placed before nouns but appear as the complement of the verb to be (The boat was afloat.) or adjectival object (After a while, he fell asleep.) of other verbs.
You cannot say: "The afloat boat sailed away." or "The asleep dog woke."
