What doesn't belong to Tai Ji Chuan's core idea is that

What does not belong to Tai Ji Chuan's core idea is to combine rigidity with softness.

Tai Ji Chuan's core idea is a kind of traditional boxing in China, which is practiced both internally and externally. Based on Taiji and the dialectical thought of Yin and Yang in China's traditional Confucianism and Taoism, it integrates many functions such as nourishing temperament, strengthening physical fitness, fighting and fighting, and combines the changes of Yin and Yang and five elements of Yi ology, Chinese medicine meridians, ancient guidance and breathing. Its core ideas include the cycle of yin and yang and the unity of man and nature. Therefore, combining rigidity with softness does not belong to Tai Ji Chuan's core thought.