The following is a sentence on an exam I gave my student this semester. It’s a lyric from the totally awesome band The Go-Go’s (who are too punk rock to care about using your lame apostrophes correctly). Read it and decide which part of speech you think sealed is: verb or adjective?
In the jealous games people play, our lips are sealed.
I first thought that sealed is clearly an adjective and that it functions as the subject complement of the sentence (a subject complement is an element required by copular verbs, such as be and seem, which does not encode a different kind of participant to the subject in the phrase in the way that an object does). But many of my students analyzed it as a verb. This calls for some weekend grammar research (while listening to the Go-Go’s of course)!
On the exam, students had to mark the function (subject, predicate, object, etc.) of each clause in the sentence. In the grammar that we’re using (English Grammar: A University Course, 2nd ed., 2006, by Downing and Locke), only verb phrases can be included in the predicate. This means that if sealed is a verb, the phrase consists of only a subject (Our lips) and a predicate (are sealed).
Two dictionaries list sealed as an adjective: the OED and Macmillan Dictionary. The OED’s citation which mirrors this construction is a bit out of date though. It comes from the 1611 printing of the King James Bible: And the vision of all is become vnto you, as the wordes of a booke that is sealed. Macmillan Dictionary only offers “a sealed box/bag/envelope” as an example. Four other dictionaries (Merriam-Webster’s, Dictionary.com, Oxford Learner’s Dictionary, and Oxford Dictionaries) do not list sealed as an adjective, only as a transitive verb (i.e. it needs an object). Strangely, Oxford Learner’s Dictionary has this example sentence under the second entry for seal as a verb:
The organs are kept in sealed plastic bags.
In this case, sealed is definitely an adjective modifying a noun (plastic bags). This must be an oversight by the editors. More importantly, though, is the fact that sealed in Our lips are sealed does not have an object. What gives?
Well, sealed is more of a participial adjective than anything else (some grammars use the terms verbal adjective or attributive verb). It’s an adjective that has been derived from a verb. Participial adjectives look like verbs but they function grammatically like adjectives. I know. Welcome to the Twilight Zone. These are the cases which really show that there are not sharp limits between the parts of speech, but rather very hazy boundaries. Sometimes it is easy to tell whether the word in question is a verb or an adjective. For example:
This is the sealed envelope that you mailed. = adjective
I sealed the envelope with a kiss. = verb
Other times – such as the one under discussion here – things are not so clear cut. Downing & Locke (p. 479) say that “past participles may often have either an adjectival or a verbal interpretation. In The flat was furnished, the participle [furnished] may be understood either as part of a passive verb form or as the adjectival subject complement of the copula was.” This means that sealed could be a passive verb that is simply missing its object. The object is presumably missing because we know that the person who owns the lips is the one who seals them, so it would sound ridiculous to say Our lips are sealed by us (although maybe not as ridiculous as the similar phrase My lips are sealed by me).
I want to argue that sealed is definitely an adjective, but like so much else in linguistics, it is hard to be definite about this. The verb analysis works just as well and sealed might be semantically closer to a verb in that we can think about the sealing of lips as resulting from an action taken. If we compare it to Our lips are chapped there isn’t as clear of an action present, except maybe the action of the weather. But I don’t like talking about verbs as action words.
For what’s it worth, 19 out of 25 people in my Twitter poll said that sealed is an adjective.
On the exam, I accepted both adjective/subject complement and verb/predicator. This made my students happy. Talking about sealed for 20 minutes in class did not make them so happy.