The difference between "I will" and "I'll" is their formalities. Contractions are generally less formal than the same two words written out.
You can use contractions in informal speech and messages, but not in formal, professional writing. Many style guides for journalism and academic writing discourage the use of contractions outside of quotes.
Further reading: http://www.everythingenglishblog.com/?p=558
Answer from kb90 on Stack ExchangeThis weekend my wife and I visited my old hometown of Conway, South Carolina (right by Myrtle Beach) to see my parents. Any time I'm back there, my Southern accent comes out and I start to use Southern-isms more frequently.
At one point, I said something along the lines of "I'm'll head inside and grab a beer." My wife (not a Southerner) had no idea what "I'm'll" meant and gave me a hard time about it. When I thought about it, I realized "I'm'll" doesn't make any sense as a contraction of "I'm" and "will," but I grew up saying it and my friends all said it too.
Does anyone have any insight as to where this contraction came from and what's going on with it? Has it been widely observed? Mainly, I just want to know my little group of redneck friends and I didn't just make it up.
word meaning - What is the difference between I'll and I will? - English Language Learners Stack Exchange
Do English-speaking people use the contractions of "will" (I'll, you'll etc.) and the contractions of "are" (you're, we're etc.) as often as the contractions of is (it's, she's etc.)? In my manuscript, I almost always contract "is", but I rarely contract "will" or "are". Will that seem weird to English-speaking readers? Should I change it?
Can "will" be contracted with any noun?
Can I use the contraction of will ('ll) with nouns??
What are contractions?
When should you use contractions?
What are some examples of contractions?
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The difference between "I will" and "I'll" is their formalities. Contractions are generally less formal than the same two words written out.
You can use contractions in informal speech and messages, but not in formal, professional writing. Many style guides for journalism and academic writing discourage the use of contractions outside of quotes.
Further reading: http://www.everythingenglishblog.com/?p=558
I'll is a contraction of I will. These types of "apostrophe words" are called contractions (though be aware that there are other reasons to use apostrophes besides forming contractions). The apostrophe indicates that one or more letters were removed, thereby shortening, or contracting, the word. In this example, I (wi)ll = I'll
As kb90 mentions, contractions are generally considered less formal, at least in writing. However, they are extremely common in speech—native English speakers use them all the time without thinking about it. In fact, they are so common that it often sounds strange, forced, or excessively formal to say "I will" in a casual conversation.
I agree with kb90'suggestions for use in writing; I would only add that "I'll" is frequently used in speech. While you will certainly be understood if you say "I will", your speech might sound a little more natural if you pay attention to and imitate the way that native speakers use contractions like "I'll".