The quick answer

Use and to add information, but to show a contrast, or to give a choice, and because to give a reason. Say I was tired but I kept working, not I was tired and I kept working.

The rule

A conjunction joins two ideas into one sentence. Choose the word by the relationship between the two ideas, not just by habit. And joins two similar or matching ideas: She is kind and generous. But joins two ideas that contrast or surprise: The bag is small but strong. Or offers a choice between two things: Choose tea or coffee. Because gives the reason for something: I stayed home because I felt ill.

Form

Examples

• He plays football and basketball.
• She is tired but she keeps working.
• Do you want juice or water?
• We left early because the traffic was bad.

Common mistakes

• ❌ I was hungry and I ate nothing. → ✅ I was hungry but I ate nothing. These two ideas contrast, so they need but, not and.
• ❌ She is kind but generous. → ✅ She is kind and generous. These two ideas match, so they need and, not but.
• ❌ Choose tea and coffee. (as an offer) → ✅ Choose tea or coffee. A choice between two things needs or, not and.
• ❌ I stayed home, I felt ill. → ✅ I stayed home because I felt ill. Two clauses need a conjunction to join them; a comma alone is not enough.