敬語は難しいので、本を買ったほうが良いでしょう。

丁寧語　is Just case of say politely any case you need speak politely (close friend or not) 尊敬語 This usage when use in position of social high or younger talk to elder 謙遜語,鄭重語 I <Family<Other Domestic<Other Foreigner this is depth of relations (in to out) we use the word In is Low, Out is High but some of word Just In is low use is basic rule other many rule here and your original judgement each group of words classify is fit for our sence unclear so case you learning case by case is better understand Polite/honorific words.