The interrelation of sciences cannot be denied. The power of reasoning and the universality of philosophical principles have paved the way for their influence on other sciences. The philosophical principle of unity (al-Wāḥid) is one of the significant and widely used principles in the science of uṣūl al-fiqh (principles of jurisprudence). There is considerable debate about its application in jurisprudential discussions. This paper uses a descriptive-analytical and critical approach to examine the validity of using the principle of unity in the science of uṣūl al-fiqh based on Imam Khomeini's philosophical and jurisprudential views. The principle of unity has been discussed in more than ten jurisprudential topics, but this paper focuses on four fundamental issues: the distinction between sciences, the accurate (ṣaḥīḥ) and general (aʿam), the obligatory alternative, and the usage of a term for more than one meaning. Imam Khomeini did not recognize the principle of unity in jurisprudential discussions. According to him, this principle is specific to the Almighty Allah, where no combination applies, and it does not apply even in mentally composite realities, let alone in composite conceptual entities.