Understanding the philosophy of science is crucial for Paper II of the UPSC exam. It helps candidates analyze and critically evaluate scientific practices, theories, and methodologies. Here are some recommended books that can aid in understanding the philosophy of science for UPSC Paper II:

1. "The Structure of Scientific Revolutions" by Thomas S. Kuhn:
- This book is a classic in the philosophy of science and provides a groundbreaking analysis of scientific revolutions.
- Kuhn introduces the concept of paradigm shifts and challenges the traditional view of scientific progress.
- It helps candidates understand how scientific knowledge evolves and the role of revolutions in shaping scientific understanding.

2. "The Logic of Scientific Discovery" by Karl Popper:
- Popper's work is essential for understanding the philosophy of science.
- This book presents the concept of falsifiability as a criterion for demarcating scientific theories from non-scientific ones.
- It explores the nature of scientific hypotheses, testing, and the process of scientific discovery.
- Popper's ideas on the growth of scientific knowledge and the scientific method are highly relevant for Paper II.

3. "Science and Hypothesis" by Henri Poincaré:
- Poincaré's book is a classic in the philosophy of science, addressing the nature of scientific theories and the role of hypotheses.
- It explores the relationship between observation and theory, the importance of intuition, and the concept of scientific probability.
- Poincaré's ideas on the nature of scientific knowledge and the limitations of empirical data are highly relevant for UPSC Paper II.

4. "The Philosophy of Science: A Very Short Introduction" by Samir Okasha:
- This book provides a concise introduction to the key concepts and debates in the philosophy of science.
- It covers topics such as induction, causation, scientific realism, and the relationship between science and values.
- Okasha's book is accessible and provides a good foundation for candidates new to the philosophy of science.

Remember, these books are not exhaustive, but they provide a solid foundation for understanding the philosophy of science. Candidates should also refer to other relevant sources and academic journals to enhance their understanding and critical analysis skills.