We know a good detective <to be/ who is> investigating the case.

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Alex_cs_gsp

Senior Member
Russian & Ukrainian
Could you tell me why infinitive can be used in the next sentences, which was taken from my test-book.

1) We know a good detective to be investigating the case. But not "We know a good detective who is investigating the case".

2) We hope this case to have been investigated. But not "We hope this case had been investigated.

3) The expert found the crime to have been commited three hours before. But not "The expert found that the crime had been commited three hours before.

4) This student was the first to be examined by our professor.


I can't find any rules why it is possible to use infinitive here. It's not an objective with the infinitive and not nominative with this one. Thanks!
 
  • Parla

    Member Emeritus
    English - US
    Could you tell me why infinitive can be used in the next sentences, which was were taken from my test-book.

    1) We know a good detective to be investigating the case. But not "We know a good detective who is investigating the case."

    2) We hope this case to have been investigated. But not "We hope this case had been investigated."

    3) The expert found the crime to have been committed three hours before. But not "The expert found that the crime had been committed three hours before."

    4) This student was the first to be examined by our professor.


    I can't find any rules why it is possible to use infinitive here.
    I've made the original sentences from your book boldface to distinguish them from your comments and alternatives.

    All of the original sentences are standard uses of the infinitive of "to be" with a passive or continuous form of the other verb.

    1) This is perfectly good wording. An acceptable alternative with the same meaning would be: We know that a good detective is investigating the case. This says nothing about our knowledge of any specific detective. Your alternative, "We know a good detective who...", has a different meaning—that we are acquainted with that particular detective, the one investigating the case.

    2) This sentence is technically correct but extremely clumsy, very poor writing. Your alternative is almost completely correct but needs present perfect instead of past perfect: "We hope this case has been investigated." That would be the right choice.

    3) Both the original and your alternative are fine.

    4) This one is also fine.
     

    Alex_cs_gsp

    Senior Member
    Russian & Ukrainian
    Could you help me to find the rules which say that we can use infinitive for such cases, because I can't find them. Thanks!
     
    Last edited:

    Thomas1

    Senior Member
    polszczyzna warszawska
    It mainly depends on the verb.
    1) We know a good detective to be investigating the case.
    Here it's the verb 'know' which allows either a that-clause or a noun phase + to infinitive clause
    know that someone/something is doing/does/etc.

    2) We hope this case to have been investigated. But not "We hope this case had been investigated.
    The verb 'hope' allows the following:
    hope that someone (different from the subject of 'hope') is doing/does/etc. e.g. We hope that this case has been/was investigated.

    hope to be doing/to do/etc. (if the subject of 'hope' is the same as the one of the verb after it, e.g. He hopes to go abroad next year.


    3) The expert found the crime to have been commited three hours before. But not "The expert found that the crime had been commited three hours before.
    Both
    find that someone/something is doing/does/etc.
    and
    find someone/something to be doing/to do/etc.
    are fine.
    You can also say:
    find someone/ something + adjective:
    The court found him guilty of the crime.


    4) This student was the first to be examined by our professor.
    This is a to-infinitive clause, you can use such clauses after oridinal numbers and adjectives in the superlative instead of the that-clauses:
    The captain was the last (one) to leave the ship. = The captain was the last (one) who left the ship.
     

    Alex_cs_gsp

    Senior Member
    Russian & Ukrainian
    Thomas and Parla you explained the difference between those sentences to me for the case when infinitive was used and when not and I could to find those rules.


    I would like to define more exactly the meaning of the sentence "The expert found the crime to have been commited three hours before." if to examine it as an example.

    The meaning of this sentence is another than the meaning of the sentence "The expert confirmed that the crime had been commited three hours before (something else happened)." I suppose infinitive can't be used for the last one because in the first sentence the expert doubts that the crime had been commited certainly three hours before but the structure of the last one says that the expert doesn't doubt, so infinitive can't be used to express this thought. Am I right?

    Thanks a lot!
     

    eyendall

    New Member
    English - Canada, UK
    Alex, I'm not sure if I understand exactly what you mean here but to me the sentence "The expert found the crime to have been committed three hours before", begs the question "before what", i.e. the sentence cannot exist alone but must be read in context.
    The same is true of the second sentence.
    Both sentences require additional information,"something else happened", to be complete. Both sentences are grammatically correct according to the context and convey the same meaning to me, but do not stand-alone. I don't think it is a matter of the investigator having any doubt: I don't read that into it all.
     

    Thomas1

    Senior Member
    polszczyzna warszawska
    Hello, Alex,

    I generally agree with Eyendall. I'll add some technical explanation to what he or she(?) says.

    The meaning of the sentences:
    1. The expert found the crime to have been commited three hours before.
    2. The expert found that the crime had been commited three hours before.
    is the same, but the structure differs a little.
    The parts:
    the crime to have been commited three hours before. (from sentence #1)
    that the crime had been commited three hours before. (from sentence #2)
    are both the direct object of the verb find (from The expert found).
    Their nature is, however, different.
    the crime to have been commited three hours before. (from sentence #1) - is a noun phrase.

    that the crime had been commited three hours before. (from sentence #2) - is a subordinate clause.

    Other than that, I can't see any difference between the two sentences. Their meaning is the same.
    [...]
    Both sentences require additional information,"something else happened", to be complete. Both sentences are grammatically correct according to the context and convey the same meaning to me, but do not stand-alone. I don't think it is a matter of the investigator having any doubt: I don't read that into it all.
    [my bolding]
    Eyendall, what do you mean by the bolded part please? That as stand-alone sentences they don't convey the same meaning meaning?

    PS: welome to the forums. :)
     

    Alex_cs_gsp

    Senior Member
    Russian & Ukrainian
    Other than that, I can't see any difference between the two sentences. Their meaning is the same.
    So if they have the same meaning it means that I can say "The expert confirmed the crime to have been commited three hours before the body was found", can't I? Based on my book I think you will find this sentence incorrect.

    With your help I found the rule why infinitive could be used for the initial sentence. That rule says that infinitive (objective with infinitive) can be used after verbs which express an assumption or hypothesis. These are such verbs as to expect, to think, to believe, to suppose, to consider, to find, to declare etc. And most often infinitive is represented by the verb to be. And there are a few example there. They are: "I consider him to be a clever man", "I suppose him to be about fifty", "I know them to be right". And realy you will find these sentences contain a part of doubt. But for me that sentence (with the expert) doesn't contain any doubt, so I thought that infinitive had been used there against the rules.

    Perhaps the example above can do this matter more clear. Are both sentences correct? "I know them to be right" and "I know twice two to be four". Perhaps you will find the last sentence is also incorrect or at least has another meaning than "I know twice two is four". I suppose you understood what I tried to say. Thanks!
     
    Last edited:

    Thomas1

    Senior Member
    polszczyzna warszawska
    It's very helpful that you provided what your book says, Alex, thank you.
    So if they have the same meaning it means that I can say "The expert confirmed the crime to have been commited three hours before the body was found", can't I? Based on my book I think you will find this sentence incorrect.

    With your help I found the rule why infinitive could be used for the initial sentence. That rule says that infinitive (objective with infinitive) can be used after verbs which express an assumption or hypothesis. These are such verbs as to expect, to think, to believe, to suppose, to consider, to find, to declare etc. And most often infinitive is represented by the verb to be. And there are a few example there. They are: "I consider him to be a clever man", "I suppose him to be about fifty", "I know them to be right". And realy you will find these sentences contain a part of doubt. But for me that sentence (with the expert) doesn't contain any doubt, so I thought that infinitive had been used there against the rules.
    Yes, indeed there is some uncertainity in a sentence which contains each of these verbs. This is, however, due to the verbs themselves. For example, if you say:
    I suspect he is the murderer. or I suspect Peter to be murderer.
    isn't equal to
    Peter is the murderer.
    The degree of uncertaininty depends of the verb itself, for example, 'know' is more sure than 'suspect'.

    Now, going back to the sentence you are concerned about.
    The expert found the crime to have been commited three hours before.
    Hearing such a sentence we, i.e. most people, usually equal it with 'The crime had been commited three hours before.' First of all, because there is the word 'expert' which gives lots of credibility to the opinion. This is a person who knows his trade and is more credible than, for example, a child. Second of all the verb 'find' contains quite a big dose of certainity. Compare these sentences:

    1. The crime had been/was commited three hours before.
    2. The expert found the crime to have been commited three hours before.
    3. The expert suspected the crime to have been commited three hours before.
    4. The child found the crime to have been commited three hours before.
    5. The child suspected the crime to have been commited three hours before.
    Even though #2 is what we usually take to mean #1 there is still some possibility that he is wrong.
     
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