이렇다, 그렇다 and 저렇다 are all adjectives. Each word is essentially the same – the only difference being the difference between 이, 그 and 저. Remember the difference between these?
이 means "this"
그 means "that" when you are referring to something in a previous sentence. For example: "I went to Canada last week. At that time I forgot about my test that I had to write."
저 means "that" when something is far from you.
이렇다, 그렇다 and 저렇다 are very important and common in Korean, so let's look at them one by one.

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LEARN KOREAN (한국어) [GRAMMAR] #1
RandomThis is book #1 for the Korean Language series. Try to understand all of the notes in this book before you proceed to the next one. Good luck ! This book contains Korean grammar. Try to understand it so that you can understand how to make a sentence...