That's a great question. First, you knew later these words start. from A,an ,the ,this ,these ,those are guide to know us the single situation or plural and to make sure something, you we said in the dialogue as you said .I will go to school then ,you didn't know any school will be there but ,if I told you the school here of course you and I knew the same school.
Keep in mind the word school has the in it.