Ok, I have been searching all the good English grammar sites (Cambridge, etc.) but to no avail. There are enough grammar geeks here at Cath Info, so I decided to bring it here after no answer was found.

I'm dealing with "if clauses" and the conditional.

I have the sentence: "We'll calculate if spaceships cost more than satellites."




Normally, the most basic "if clauses" are conditionals of imaginary outcomes that require the sentence structure if clause>simple present tense/comma/main clause>future tense. Or they can come in some other varieties of verb tenses.

At first glance, it would seem that this "if clause" follows this pattern...future will and simple present tense. But this is a real result that will be determined. In this case, Cambridge gives the option of repeating will future in both tenses, or even using the conditional auxiliary "would" and others. (We will calculate if spaceships will cost more than satellites.) I don't suppose that either the repeated use of "will" or the "will" combined with simple present are incorrect.

My issue is in trying to determine why this sentence can not be inverted with the "if clause" coming at the beginning and offset with a comma. Obviously, it is incorrect to say: "If spaceships will cost more, we will calculate." The collocation is very much off, but where is the official rule on this? What are the circuмstances that dictate when an "if clause" can be inverted (the majority of if clauses), and when can they not be inverted? What is the rule for this called? There is virtually no information to be found to explain this. As a native speaker, my only explanation would be to say that it doesn't sound right. This can't be right. There has to be a rule somewhere for determining when "if clauses" cannot come at the beginning of the sentence and an actually grammatical term for this.

Any help is greatly appreciated.

Here is a good link from Cambridge... http://dictionary.cambridge.org/pt/gramatica/gramatica-britanica/conditionals-if

Cambridge does not touch on the theme of when it is incorrect to invert the clauses.

Technically, it's not a conditional sentence and therefore not an if clause. You are presenting two alternatives. While my instinct is to change "if" to "whether", I'm not entirely sure if that's required.

Yes, "whether" was included as an equal alternative to the same sentence. However, it was erroneously labeled as an "if clause" with the rule following the imagined situation. (This much I knew to be incorrect.)

What you say makes sense about presenting two alternatives: they either cost more or they don't. Is there any particluar grammar rule that you can point me to in this regard. Thanks in advance.

According to Cambridge, it is only incorrect to use "if" if you try to combine it with "about if". In that case, you must use "whether".  It's an interesting article for grammar heads.

http://dictionary.cambridge.org/grammar/british-grammar/if-or-whether


If and whether: indirect questions
We can use if or whether to report indirect yes-no questions and questions with or. If is more common than whether:

Call the bakeries around town and find out if any of them sell raspberry pies.

I rang Peter from the station and asked if I could drop in to see him before going back or if he’d meet me.

We often prefer whether in more formal contexts:

The teachers will be asked whether they would recommend the book to their classes.

Neil Obstat is correct that the sentence is ambiguous.  In colloquial English, the sentence would probably be understood in context, but as a stand-alone statement, it could indeed mean that we are only going to calculate (some undefined calculation) if spaceships cost more but won't calculate if they do not.

In context, such an understanding could indeed be the correct understanding.

If we are trying to calculate which costs more (i.e., spaceships or satellites), then the sentence should use "whether" instead of "if".

Thanks Neil. I didn't include that in my post, but it was the first thing that I mentioned on #slack. I'm referring to the ambiguity. I proposed that the answer combine the future will with an infinitive like: "we will calculate to find out if..." or "we will calculate to see if...".  The ambiguity was the first thing that I noticed. There is no doubt that the company in question will have to change this. Right now, they are busy defending it as a "conditional if phrase". Cambridge gives great information, and you will notice that some of the noun clauses actually do combine the will future clause with an infinitive, so I think this confirms what we are both saying here.


The difference in the two examples is that one example is a noun clause, and the other one is an "if clause". The "if clause" can be inverted and a comma added, and the other meaning would be a noun clause and cannot be inverted.

If we are trying to calculate which costs more (i.e., spaceships or satellites), then the sentence should use "whether" instead of "if".

Here are the rules from Cambridge that says your assertion is incorrect. If you have another respected source that states something different, I kindly ask you to share it with us.

To express an alternative, we can use or not with if and whether. With whether we can use or not immediately after whether or in end position. With if we use or not in end position only:

I called Bill to find out whether or not he really did go to Afghanistan.

I called Bill to find out whether he really did go to Afghanistan or not.

I called Bill to find out if he really did go to Afghanistan or not.

("Find out" is a phrasal verb here and is not a preposition in this case-Centro)


We use whether and not if before a to-infinitive, often when we’re referring to future plans or decisions:

I was wondering whether to go for a swim.

Some financial decisions, such as planning a pension, need to be taken as early as possible. Others, such as whether to move house, can probably only be made much later.

We use whether and not if after prepositions:

Later I argued with the doctor about whether I had hit my head, since I couldn’t remember feeling it.

Not: Later I argued with the doctor about if I had hit my head …

The police seemed mainly interested in whether there were any locks on the windows.

Not: The police seemed mainly interested in if there were any locks

http://dictionary.cambridge.org/grammar/british-grammar/if-or-whether