Answer: Sin is any want of conformity unto, or transgression of, any law of God, given as a rule to the reasonable creature.₁

1. 1 John 3:4; Galatians 3:10,12

For further study see:

1. WSC 14:  What is sin?
2. Elder Gregory Moeck of First Presbyterian Church, San Francisco on WLC 24a: “Why sin consists chiefly in our rational faculties:
   
3. Elder Gregory Moeck of First Presbyterian Church, San Francisco on WLC 24b: “Practical consequences of sin consisting chiefly in our rational facilities”
   
4. Elder Gregory Moeck of First Presbyterian Church, San Francisco on WLC 24c – How can I know if something is sinful and how can I avoid those things?
   
5. WSC 15: What was the sin whereby our first parents fell from the estate wherein they were created?
6. WSC 18: Wherein consists the sinfulness of that estate whereinto man fell?
7. WSC 20: Did God leave all mankind to perish in the estate of sin and misery?
8. WSC 84: What doth every sin deserve?
9. WSC 85: What doth God require of us, that we may escape his wrath and curse due to us for sin?
10. WLC 25: Wherein consists the sinfulness of that estate whereinto man fell?
11. WLC 26: How is original sin conveyed from our first parents unto their posterity?
12. WCF CHAPTER 6: Of the Fall of Man, of Sin, and of the Punishment Thereof