I've seen this video about the grammar of writing commas and I'd like to write a sentence of this type:

I think this will be a good year, I'm sure of it. (wrong)

But I know you can't just put two sentences together without a linking word. What is the best way to write the sentence, to make a sentence as clear as possible for the reader?

a) I think this will be a good year. I'm sure of it.

b) I think this will be a good year - I'm sure of it.

c) I think this will be a good year, and I'm sure of it.

  • 4
    There is no "grammar of writing commas" in English, and anyone who claims that there is should be called out as a charlatan. There are several "style guides" which provide useful recommendations for the use of the comma, but there are no immutable "rules" which govern its usage. All of your examples are perfect, idiomatic, and understandable—including the one you think is "wrong". Jul 8, 2017 at 9:17
  • @P.E.Dant And to add a charlatanic note to your observation: even the style guides I'm familiar with would call OP's "wrong" sentence okay. "He'll be here, I'm sure of it!" The expression is very much natural to dialogue anyway, and that in genres that privilege realistic intonation like that comma signals (compared to a stronger break). Jul 8, 2017 at 14:24

2 Answers 2


All of your answers are acceptable. The example that you call "wrong" is a comma splice, and many style guides recommend avoiding comma splices.

There is another solution: You can use a semicolon to indicate two sentences are closely related.

I think this will be a good year; I'm sure of it.


In your "wrong" sentence, "I'm sure of it" is functioning similar to other filler phrases (for lack of a better term) in the spirit of "you can bet", "for sure", "certainly", "of course", and others. As far as I know, all of those can be inserted pretty much wherever it makes sense, thus justifying your example (although repeating with "it" is awkward). There are many great ways to write this sentence, and here are some I could come up with.

I think this year will be a good year; in fact, I'm sure of it.


I'm sure this year will be a good year.


I think this year will be a good year, I'm sure


Surely, I think, this year will be a good one (replacing "a good year" with "a good one" is relaxed but perfectly fine).


This year will be a good one, I'm sure of it!

Your example c) is awkward; it doesn't mke sense to use "and" there to compound on your "I think" with "I'm sure". "And" can be used there for different things "I think [...] and I'm sure it will be better than last year," but it's repetitive here to conjoin like that.

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