Necessarily means that something must be true or must happen because of logic, rules, or the nature of things. It's the opposite of “possibly” or “maybe.” When something is necessarily true, there's no way around it.

If you have a square, it necessarily has four sides. That's part of what makes a square a square: it must always be true. If your teacher says, “Anyone who scores below 70% will necessarily have to retake the test,” she means there are no exceptions: the rule applies to everyone in that situation.

The word often appears when people want to challenge assumptions. If your friend says, “Smart people are good at math,” you might respond, “That's not necessarily true.” You're pointing out that while some smart people excel at math, being smart doesn't automatically mean you're good at math. One thing doesn't necessarily lead to the other.

In everyday conversation, necessarily helps us think more precisely. It pushes us to ask: Does this always follow? Must this be true? Or are we just assuming it is? When you say something isn't necessarily so, you're opening the door to other possibilities and keeping your thinking flexible.