If birds did not have wings

[patanjali.purpose]

If birds did not have wings, they would not have been able to fly
a) If birds did not have wings, they would not have been
b) If birds had no wings, they would not have been
c) Unless birds had wings, they would not be
d) If birds did not have wings, they would not be
e) Unless birds had wings, they would not have been

C vs D

[sam2304]

C - Usage of unless in third conditional is wrong. We need present tense when we use unless i suppose.

IMO D.

[avik.ch]

Unless = if not

If our train is on time, we will arrive at 7.
If our train is not late, we will arrive at 7.
Unless our train is late, we will arrive at 7.

but there are certain sentence where this can't be applied : A took place if it's not stopped by B. here "unless" cannot be used

The global definition of "unless" is ( except if - circumstances ) - its the other way of looking at it.

I'll be at your place at 9.00, unless [= except if, circumstances] the train is late. -- In this sentence there is only one reason why I might be prevented from being at your place at 9.00, and that would be the train being late

Since here there is no as such circumstances -- "If" is apt in D.

What is the OA ?

[patanjali.purpose]

Unless = if not

If our train is on time, we will arrive at 7.
If our train is not late, we will arrive at 7.
Unless our train is late, we will arrive at 7.

but there are certain sentence where this can't be applied : A took place if it's not stopped by B. here "unless" cannot be used

The global definition of "unless" is ( except if - circumstances ) - its the other way of looking at it.

I'll be at your place at 9.00, unless [= except if, circumstances] the train is late. -- In this sentence there is only one reason why I might be prevented from being at your place at 9.00, and that would be the train being late

Since here there is no as such circumstances -- "If" is apt in D.

What is the OA ?

I am very curious to understand UNLESS construction. IMO we can use UNLESS in the example you provided: A took place UNLESS IT's stopped by B. . Unless is just a substitUte for IF NOT

What do you think.

What is the difference btn HAD (in C) vs DID HAVE (in D).

OA - C

[avik.ch]

I am very curious to understand UNLESS construction. IMO we can use UNLESS in the example you provided: A took place UNLESS IT's stopped by B. . Unless is just a substitUte for IF NOT

What do you think.

I think I already wrote the usage of "unless" vs "if" ---

If we consider unless = if not , then both C and D are correct. What is the official Explanation, is it concision ?

A took place UNLESS IT's stopped by B. -- is correct if you personally want to make the "being stopped by B" is a circumstances. This is much more dependent on the writer's intent.

But,

I cannot understand how birds having wings is a circumtances here-or may be !! I am not sure. What is the source of this SC ? Can you please invite any expert ?

What is the difference btn HAD (in C) vs DID not HAVE (in D).

No difference(please dont omit the "not"). This is the way of converting a sentence in to a negative form. The point to be noted here is that the first verb always takes the tense form and the s-v agreement,while all others be in their base form.

will have done( present prefect conditional) -----------> would have done ( past perfect conditional)
have/has done ( present perfect) -----------------------> had done ( past perfect )

When we have a main verb - we just add "not" to convert it into negative form

I have a book ----> I do have a book ----> I do not have a book.
I had a dream -----> I did have a dream ------> I did not have a dream.

In both, only first verb takes the tense form : and all other remain in its base form. This is the way the construction of the verb takes place.
https://www.beatthegmat.com/mgmat-sc-dou ... tml#445245

Hope this helps !!

[dario.brignone]

IMO the benefit of using "unless" instead of "if not" is that we avoid two negations in the same sentence, thus making it easier to be understood.

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If birds did not have wings, they would not have been able to fly
a) If birds did not have wings, they would not have been
b) If birds had no wings, they would not have been
c) Unless birds had wings, they would not be
d) If birds did not have wings, they would not be
e) Unless birds had wings, they would not have been


Avik is absolutely right. 'Unless' is used for certainity or when words like 'will' is used.

According to me the answer should be D. A strong D. I think there is something wrong with the OA or maybe the source.

Just recheck it once.

May be some expert should really help in here...

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Also 'Unless' is used for doing some routine or daily work. Yes it is indicative of an habitual result. So the answer is a confirm D. Yes Avik's explanation is perfect...

Unless cannot be used in the first conditional. Also if you see other 2 conditionals, you will see that the word 'would' is used in the 2nd and the 3rd conditional...

The current sentence is about ability and not routine or specific circumstance.

I hope this explanation really helps.