`凡是` is more of a grammatical tool than a deeply cultural term, but its usage reflects a pattern of thinking that involves categorization and the application of universal principles. It's frequently found in formal contexts like legal documents, official announcements, and company policies, where clarity and the absence of exceptions are crucial. In a broader sense, it's also used in philosophical statements and proverbs to convey timeless truths. For example, the famous quote, “凡是存在的，就是合理的” (fánshì cúnzài de, jiùshì hélǐ de) - “Whatever exists is reasonable,” uses this structure to make a profound, sweeping statement about reality. This can be contrasted with the simple English word “all.” While “all students” (`所有学生`) simply points to a group, “凡是学生…” (“All who are students…”) sets up a conditional framework. It implies: “If you meet the criteria of being a student, then the following rule applies to you.” This focus on criteria and universal application gives `凡是` a more formal and logical weight than a simple quantifier.
`凡是` is common in both written and spoken Mandarin, though it carries a slightly more formal or emphatic tone than everyday alternatives.