18.090 is infamous for its short, frequent quizzes (every 1–2 weeks). A typical quiz question: "Write the negation of the following statement: For every ε > 0, there exists a δ > 0 such that if |x - a| < δ, then |f(x) - f(a)| < ε." (The epsilon-delta definition of a limit). Students tremble—not because of calculus, but because of the logical nesting of quantifiers.
The course is typically taken after single-variable calculus (18.01) and before real analysis (18.100) or abstract algebra (18.700). Its credit load is 3-0-9 (3 class hours, 0 lab hours, 9 expected study hours per week), reflecting MIT’s intensive unit system. 18.090 introduction to mathematical reasoning mit