The discussion centers around the book "Thermodynamics and an Introduction to Thermostatics" by H. Callen, with mixed opinions on its suitability for beginners in thermodynamics. One participant praises Callen for its mathematical formalism and ability to connect physical concepts with mathematics, recommending it alongside other complementary texts such as "Concepts in Thermal Physics" by Blundell, "Thermodynamics" by Fermi, "Understanding Thermodynamics" by Van Ness, and "Classical Thermodynamics" by Pippard. Another contributor acknowledges Callen's historical significance but argues it may not be the best starting point due to its heavy focus on mathematics, suggesting that it could lead to misunderstandings, particularly regarding concepts like enthalpy. They recommend using Cengel for more quantitative approaches. The conversation reflects a broader debate on the balance between mathematical rigor and conceptual understanding in learning thermodynamics.