Which "if" is appropriate for what situations

Question

As a follow up to "What is the difference between 假如 and 例如?" I've become unclear on the use of the if statement in Chinese.

For the most part I would use 如果 as an if statement when ever it's required but I have now stumbled across a few:

假如 Jiǎrú - if 
要是 Yàoshi - if
若是 Ruòshì - if
如果 Rúguǒ - if / in case / in the event that
倘 Tǎng - if / supposing / in case
倘若 Tǎngruò - provided that / supposing that / if
假若 Jiǎruò - if / supposing / in case
假使 Jiǎshǐ - if / in case / suppose / given ...

Translations from MDBG

All these translate into "if" so how are they used differently or are they interchangeable?

Answer 1

假如 Jiǎrú - if

Generally used. In most case, it's for something that wouldn't happen.

要是 Yàoshi - if

Mostly used in 最近雾霾这么厉害，要是我离开北京就好了 - It'd be great if I had left Beijing! The air pollution is so heavy here.

若是 Ruòshì - if

Literally used, similar to 要是

如果 Rúguǒ - if / in case / in the event that

Generally used.

倘 Tǎng - if / supposing / in case

Almost only used in literature works.

倘若 Tǎngruò - provided that / supposing that / if

Mostly used in love letters or lyrics.

假若 Jiǎruò - if / supposing / in case

Seldom used. A bit like 假如

假使 Jiǎshǐ - if / in case / suppose / given ...

Seldom used.

Answer 2

They are pretty much interchangeable, 如果,假如,假使,要是 are more common used ones, as a native speaker, I rarely hear 倘, only saw it in literature books.