Let’s start with a pair of endings that many people find confusing: -able and -ible. These suffixes are usually used to form English adjectives. They sound very similar when you say them and they share a main meaning, which is ‘able to be’: readable able to be read; easy to read eatable able to be eaten; fit to be consumed as food audible able to be heard collapsible able to be folded into a small space

There is no difference in modern English usage. The pronunciation is very similar. Words ending in '-ible' are generally older words. Words ending in '-able' may be newer. Unfortunately, that does not mean that both spellings are correct when it comes to individual words and there are no tricks to help students learn which is correct. If you're not sure, you'll have to check a dictionary.

As far as I understand, you simply have to learn which suffix to use. After a while, you'll be able to know intuitively.

Is this link helpful? http://grammarist.com/usage/able-ible/