Hello, fellas. On this Chinese Lunar New Year’s Day, we will discuss other forms of conditional sentences. According to Betty Schrampfer Azar, a conditional sentence usually comprises of an adverb clause of condition or if-clause, which contains a condition, and a result clause, which shows a result.
(More on conditional sentences: https://englishtips4u.com/2018/06/04/engclass-conditional-sentences-revisit/)
There are other words introducing adverb clauses of condition.
1) Whether or Not and Even If
Whether or not and even if mean that the result will be the same despite the condition.
I am going to go the beach tomorrow whether or not it rains. (Or whether it rains or not)
I am going to go the beach tomorrow even if it rains.
(If it rains, I am going to the beach. If it does not rain, I am going to the beach. I do not care about the weather. It does not matter.)
2) In Case and In the Event That
In case and in the event that show that something will probably not occur, but it might. In the event that is more common in formal usage than in case.
I will be online in case you need to contact me.
I will be online in the event that you need to contact me.
Unless has the same meaning as if…not.
I will go to the beach tomorrow unless it rains.
I will go to the beach tomorrow if it does not rains.
4) Only If
Only if expresses the idea that only one condition will lead to a particular result. The subject and verb of the result clause are inverted when only if begins a sentence.
The picnic will be cancelled only if it rains.
Only if it rains will the picnic be cancelled.
(More on inversion with negative words: https://englishtips4u.com/2012/11/06/engclass-inversion-sentences-begin-with-negative-adverbs/ and https://englishtips4u.com/2018/11/21/grammartrivia-inverted-subjects-and-verbs-with-negative-expressions-or-comparisons/)
Betty Schrampfer Azar, Understanding and Using English Grammar: Third Edition