A technical distinction matters here: the book contains three disciplines, but the introduction treats the science of balagha in a narrower sense through Maʿani and Bayan. Badiʿ then studies embellishments of expression.
ExpressionMeaning in this discussion
Three disciplinesMaʿani, Bayan, Badiʿ
Science of balaghaIn this technical division: Maʿani and Bayan
Third disciplineBadiʿ
Thus 'two constituent sciences of balagha' and 'three disciplines in the text' refer to different scopes.
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Introduction: Structure, Three Disciplines and Kinds of Preface
A technical distinction matters here: the book contains three disciplines, but the introduction treats the science of balagha in a narrower sense through Maʿani and Bayan. Badiʿ then studies embellishments of expression.
ExpressionMeaning in this discussion
Three disciplinesMaʿani, Bayan, Badiʿ
Science of balaghaIn this technical division: Maʿani and Bayan
Third disciplineBadiʿ
Thus 'two constituent sciences of balagha' and 'three disciplines in the text' refer to different scopes.