Since is a word that connects events in time, showing that something started in the past and continues to affect the present. When you say “I've been reading since breakfast,” you mean you started at breakfast and you're still reading now. When someone says “Since you're already going to the store, could you pick up milk?” they're using one fact (you're going to the store) as the reason for their request.

The word works in two main ways. First, it marks a starting point: “She's lived in Boston since 2015” tells us when something began. Second, it explains why something is true: “Since it's raining, we'll play inside” means the rain is the reason for the decision.

Notice how since differs from because. While both can explain reasons, since often feels gentler and more matter-of-fact. Compare “Because you broke the rules, you're in trouble” with “Since you're interested in space, you might like this book.” The first sounds like a judgment; the second sounds like a helpful connection.

Writers sometimes start sentences with since to create flow between ideas: “Since we'd already finished our homework, we had time to build a fort.” This connects the completion of homework to the fort-building in a smooth, logical way.