This book is part of a series composed of 4 books: “Measures in Music”, “Intervals in Temperament & Arel-Ezgi Systems”, “Scales, Modes & Maqam Scales” and “Chords & Fourth Harmony Chords”. This study is divided into two main sections; first main section is on the conventional chords in western musical tradition and the second one is on the fourth harmony chords which are functional in the harmonisation of a set of maqam scales which can be expressed in the temperament system. In each main sections there exist 3 subsections including i- the theoretical explanations on the constitutions of relevant chords, ii- demonstrations of chords on certain scale structures (such as modes or maqam scales) and iii- a set of chord progressions. At the end of the second main section (on fourth harmony chords) there is an other subsection including the graphical illustrations of fourth harmony chord positions on guitar. In this book, at the proper places under the relevant titles, the contents of the Audio CD (which will be distributed via Internet) is also illustrated for the reader and the notation of listening samples are presented in the form of either conventional notes or of tables.