There's a bird on the lawn that I think must be a nightingale come over on the Cunard or White Star Line.
According to my very limited knowledge, shouldn’t it be "which came over" in place of "come over"?
By this logic is it grammatical to say: "There’s a chicken come over on a plane"?
It's an example of a reduced relative clause
A reduced relative clause is a relative clause that is not marked by an explicit relative pronoun or complementizer such as who, which or that. An example is the clause I saw in the English sentence This is the man I saw. Unreduced forms of this relative clause would be "This is the man that I saw." or "...whom I saw." Wikipedia
EDIT 15/03/23
(Many thanks to @Stef in the comments) I hadn't considered the fact that F.Scott Fitzgerald would have used be to form the perfect with the intransitive verb ‘come’ in “a nightingale is come over on the Cunard…”. Although The Great Gatsby was published in 1925, nearly a hundred years ago, I wasn't aware this construction, at least in American English, was still in use at the time and some native speakers would consider ‘come’ in ‘come over’ as an adjective.
Dictionary.com says [emphasis mine]
- (used in archaic or literary constructions with some intransitive verbs to form the perfect tense):
He is come. Agamemnon to the wars is gone.
Wiktionary offers this quote from Shakespeare's Macbeth, 1601
- They are not yet come back.
instead of the modern They have not yet come back.
From the 1722 novel, Moll Flanders, by Daniel Defoe; we have two examples of the perfect tense used in the same excerpt.
but at his Defire I altered that Resolution, and he is come over to England alfo, where we refolve to spend the Remainder of our Years in fincere Penitence for the wicked Lives we have lived.
From The Tenant of Wildfell Hall written by Anne Brontë in 1848
I went down to dinner resolving to be cheerful and well-conducted, and kept my resolution very creditably, considering how my head ached, and how internally wretched I felt. I don't know what is come over me of late; my very energies, both mental and physical, must be strangely impaired,…
In The Great Gatsby quotation, the modernised version would be:
…that I think must be a nightingale [which has] come over on the Cunard or White line
The relative clause with a present perfect construction could be replaced with ‘having’
…that I think must be a nightingale having come over on the Cunard or White line.
The sentence uses ellipsis to convey meaning in an economical way. Although formal grammar might require "that has come over" or "that came over", the meaning is unambiguous and clear without such expansion of the text. The following general quotation from the Cambridge dictionary also serendipitously deals with your specific concern about the missing "which" or "that":
Cambridge
Textual ellipsis:
When we can easily understand everything in the sentence because of the surrounding text, we use textual ellipsis. For example, we know that certain verbs and adjectives can be followed by a that-clause, so if we see a clause without that after such verbs and adjectives, we assume that the writer or speaker wants us to understand the same meaning as a that-clause:
I knew [that] something terrible had happened.
If meaning is clear and unambiguous, insistence on formal grammar may merely seem pedantic and plodding. This raises the question of what should be the philosophical and operational basis of formal grammar; but that is too broad a topic to be tackled here.
This must be rain falling from the sky. (Said while the rain is falling.)
This must be rain fallen from the sky. (Said after it has fallen.)
The word "come" in the quoted sentence is syntactically parallel to "fallen" in this example.
In English, past participles are usually passive participles, but in these examples they are being used as active participles. The present participle, "falling", is unambiguously active rather than passive.
