Your v. You're
Oh god, THIS mistake. I've seen people make it a lot, and it's sadly very common.
Your- this describes ownership. Ex: Your dog, your boyfriend, your idea, your sister, your life.
You're- a contraction of "you" and "are". If you're not sure which term to use, try "you are" before what you're going to say, and if it works say "you're" and if not say "your". Ex: You're very pretty, you're my favorite friend, you're next door to Kathy, you're a student.
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There v. Their v. They're
Three different spellings, yet they're all pronounced the same.
There- this describes a location. Ex: I live there, she sat there, we went there, she's going there.
Their- this describes ownership. Ex: Their family, their cat, their teacher, their food, their siblings.
They're- a contraction of "they" and "are". Use the same trick I told you to use with "you're". Try "they are" before what you're going to say, and if it works say "they're". You can then decide if what you're talking about is a location or not. If you are, use "there", if not, use "their".
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Know v. Now
Know- it's when you have information, I suppose. Ex: I know how to write now, I don't know how to dance, I know how to make good mad 'n cheese.
Now- the time currently. Ex: Now, I will help you write. I can't tell him now because he's mad at me, now is the time to write.
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I'm somewhat running out of ideas, so PLEASE, if you need help with something, PM me or comment with your question and I'll answer it in the next chapter.