"A Defence of Free-Thinking in Mathematics" is an influential work by the philosopher George Berkeley, published in 1735. In this book, Berkeley argues against the prevailing views of mathematics and the philosophical assumptions that underlie them. Berkeley begins by challenging the notion that mathematics is a purely deductive science, separate from empirical observation and contingent on the existence of material objects. He criticizes the reliance on abstract concepts such as points, lines, and numbers, which he believes have no basis in reality. Instead, Berkeley advocates for a more empirically grounded approach to mathematics, one that is rooted in sensory experience and concrete phenomena. Central to Berkeley's argument is his rejection of the existence of abstract entities, including mathematical objects, outside the mind. He contends that mathematical truths are not discovered but rather invented by the human mind and that they are ultimately dependent on our perceptions and conceptual frameworks. Furthermore, Berkeley contends that the use of infinitesimals and other mathematical concepts that cannot be directly observed or measured introduces ambiguity and uncertainty into mathematical reasoning. He advocates for a more rigorous and intuitive approach to mathematics, one that is free from the speculative assumptions of traditional mathematical philosophy. Overall, "A Defence of Free-Thinking in Mathematics" presents a radical critique of the foundations of mathematics and challenges readers to reconsider their assumptions about the nature of mathematical knowledge and truth. It remains an important work in the philosophy of mathematics and continues to provoke debate and discussion among scholars to this day.