If you were asking about the distances, then こ is something in your immediate vicinity. そ is something that is in the middle between こ and あ. It's something that you can point to and people know what you're pointing to. あ is something really far away that you try to point to, but people might know exactly where you're pointing to. Basically the idea of where that thing is becomes more and more vague as you go from こ to あ。 これ、それ、あれ are followed by particles. It might be easier to think of this set as a noun/pronoun. これは難しいです。それが簡単です。あれは面白そう。 This is difficult. That is easy. That (way over there) seems interesting. この、その、あの are followed by a noun. It be easier to think of this set as an adjective. この犬は太すぎる。その猫は寝ています。あの人のことをよく思っています。 This dog is too fat. That cat is sleeping. I often think of that that person (way over there). The same rule for どれ and どの , but they are the question you would ask to get one of the above answers. どれが難しいですか。Which one is difficult？どの猫が寝ていますか。Which cat is sleeping? Best of luck!