introversion vs. extroversion, sensing vs. intuition, thinking vs. feeling, and judging vs. perceiving. Each person has a preference for one of these dichotomies, which helps to determine their personality type. By observing someone's behavior and decision-making processes, it is possible to get a sense of which dichotomies they prefer.
It's worth noting that while the MBTI personality assessment is widely used and can be a useful tool for understanding oneself and others, it is not a scientifically validated test. It's important to keep this in mind when using the MBTI to identify someone's personality type, and to avoid making assumptions about people based solely on their personality type.