I am confused about using the future tense in noun clauses versus time clauses.

I know that the future tense is not used in time clauses, but that it can be used with noun clauses.

However, I am having trouble differentiating between noun clauses and time clauses in a sentence such as:

  1. I know when he will come.
  2. I will buy this when he asks me to.

In those two sentences, how can I determine that the dependent clause is acting as a noun clause and not as a time clause?


I am sure that deadrat's answer is authoritative and complete, but I am going to give you a simpler approach in case you are having trouble with deadrat's. Maybe mine will be too simple -- let's see.

For each of your sample sentences, let's see what type of question fits. We should try to write a when question if we can. If that doesn't work, then we'll write a when question.

I will use your example sentences, but with a few little changes.

Statement 1: Mama knows when Ricky will come.

Question 1: What does Mama know?

A "when" question wouldn't work here, so we write a "what" question.

Statement 2: Bruno will buy the new sofa when Papa gives him the money for it.

Question 2: When will Bruno buy the new sofa?

A "when" question works, so we stop there.

  • 1. I think you should make clear that a what question means you're dealing with an object and a when question means you have an adverbial modifier of time. 2. I think you mean If that doesn't work, then we'll write a what question. 3. You can stop at when with Bruno, but a "what" question wouldn't work if you didn't. I like it enough to upvote it. – deadrat Dec 8 '16 at 7:55
  • @deadrat - Please feel free to edit my answer -- if you don't feel like it, I will but later. – aparente001 Dec 8 '16 at 17:52

Alas, the answer is context, both syntactic and semantic. This answer may be unsatisfying because it doesn't give a general rule. But let's look at your examples. For the sentence

I know when he will come.

the subordinate clause is the direct object of know (and thus a noun clause). It can't be an adjunct, that is, a modifier of know, because know is present tense, and it's hard to see how a future action, one that hasn't happened yet, can affect the manner of knowing now. It's possible, however to construct an ambiguous sentence. Consider the following exchanges, perhaps from trial testimony:

Q1: What did you know about the robbery?
A1: I knew when he robbed a bank, but I didn't know which bank.

Noun clause: what I knew.

Q2: When did you realize he was dangerous?
A2: I knew when he robbed the bank, but not before.

Adverbial adjunct of time: when I knew.

Note that to know has a strong attraction for an immediately following direct object. You generally don't leave out what you know, unless it's clear from context:

Q3: Do you know that your shoe is untied?
A3: Yes, I know.

Clearly meaning I know that my shoe is untied.

Which is why A2 would more likely be phrased as

A2a: When he robbed the bank, I knew, but not before.

In your second example

I will buy this when he asks me to.

you know that the subordinate clause is an adjunct and not an object for two reasons. First, because this occupies the slot of direct object (the thing bought). If buy is to be used ditransitively, i.e., if it is to take a second object, such a second object must be an indirect object (the receiver of the purchase):

I will buy him this.

But a when clause can't mean a receiver of a transfer.

Secondly, the clause when he asks me to names a point in time, which is not a thing you can buy. So even if the sentence didn't already have a direct object, a point in time wouldn't make a suitable substitute direct object.

Thus with the clause precluded as an object, it must be an adjunct.

  • @Rathony Did the edit take care of it? – deadrat Dec 6 '16 at 21:04
  • Not sure what the problem was, but I don't see any errors. Great answer, but would suggest fleshing out the part at the very end. – aparente001 Dec 6 '16 at 23:52
  • @aparente001 Can you give me an idea of what you think is lacking or unclear. Thanks. – deadrat Dec 7 '16 at 16:33
  • Sure. "couldn't serve because it isn't" -- What couldn't it serve as? What is "it"? In a thorough, carefully written answer like this, why not spell it out more clearly for the bleary-eyed. – aparente001 Dec 7 '16 at 17:15
  • @aparente001 Clearly someone bleary-eyed wrote the original. Clear as mud. I've tried a rewording. Check to make sure I haven't made things worse. Be sure to include @ nym for me so I get pinged. – deadrat Dec 8 '16 at 4:16

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