Because is a word that introduces the reason for something. When you explain why something happened or why you did something, you often use because to connect the effect to its cause.

If your teacher asks why you're late to class, you might say, “Because I missed the bus.” The word links your lateness (the effect) to missing the bus (the cause). When your friend asks why you're smiling, you might answer, “Because I just got a new puppy!” The smile is the effect, the puppy is the reason.

Notice how because points backward to explain something that already happened or already exists. It's different from words like “so” or “therefore,” which point forward to show what will happen next. Compare these: “I studied hard, so I did well on the test” versus “I did well on the test because I studied hard.” Same facts, different direction of explanation.

People sometimes string together weak reasons using because when they're making excuses. Strong reasoning requires real causes: “I finished my homework early because I started right after school” is more convincing than “I didn't finish because it was hard and I was tired and my pencil broke.”