What is a Conditional?
A grammar device that shows possible results from certain situations is called a “conditional.” The presence of the word “if” will usually call attention to them, and some have actually nicknamed them “if” sentences. There are several types, but three “basic conditionals” are used most frequently.
This situation is in the future and has a real possibility of happening.
“If Bob comes over, we will watch the game.”
There is a good likelihood that Bob will come over.
The second also refers to the future but is quite unlikely.
“If I went to the moon, I would know if it is made of cheese.”
It is highly improbable that the speaker will visit the moon.
Unlike the first two, this refers to the past and cannot happen.
“If Jill had gone to the zoo, she would have taken pictures.”
This is in the past and cannot be fulfilled; Jill did not go to the zoo and so her photos are an impossibility.
Whether or If
These are often interchanged but actually have different uses. When showing a condition, use “if,” but when showing a choice or alternatives, use “whether.”
“If” implies that the result depends on one specific condition.
“We will go for a walk if it doesn’t rain.”
“If you finish you dinner, you can have some pudding.”
“Whether” shows choices or alternatives and generally requires an “or.” “Or not” is often used for yes/no choices; some consider “or not” redundant and some see it as more formal. “Whether” by itself can hint at both positive and negative possibilities.
“Tell Rachel whether you want chicken or beef for dinner.”
“Whether or not you are going to the party, please call.”
“Let us know whether the school is open.”
SHOULD YOU CALL?
When the speaker only wants you to call if you’ll be there:
“Please call if you are going to Perkie’s Pizza on Friday.”
When the speaker wants you to call either way:
“Please call whether or not you are going to Perkie’s Pizza on Friday.”
“Please call whether you are going to Perkie’s Pizza on Friday.”
To Sum it Up
Is there a result that relies on certain conditions? Use “if.”
Is there some sort of choice? Use “whether.”
Should “or not” be used with “whether?” Some do, some say “sometimes” and some say “don’t bother.” What is your opinion?
http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/2cond1.htm (2nd conditional)
http://www.better-english.com/grammar/cond2.htm (2nd conditional)
Inversion cases in conditional sentences: