Criminal Law (Substantive)
Core concepts
Master the elements of an offense: the prohibited act (actus reus), the mental element (mens rea), causation, and the absence of a justification or excuse. Distinguish intent, knowledge, recklessness, and negligence, and know which offenses require which. Understand participation: principal, accomplice, instigator, and accessory after the fact, and the rule that an accomplice's liability is derivative of the principal act. Study inchoate offenses (attempt, conspiracy, solicitation) and when preparation becomes attempt (a direct step toward the act). Learn the grounds that remove wrongfulness (self-defense, necessity, lawful arrest, consent where recognized) and those that remove culpability (minority, insanity, mistake of fact).
Traps
Examiners love the distinction between mistake of fact (may excuse) and mistake of law (generally does not). Another trap is self-defense: the force must be necessary and proportionate to the threat, and the defender cannot be the aggressor. Watch for questions on causation where an intervening act breaks the chain. Also be careful with attempt - mere preparation is not enough.
Rule of thumb
For any offense question, build a checklist: Act? Mental element? Causation? Justification? Excuse? If any element is missing, the offense fails, but a lesser included offense may still apply.
Worked example
A man takes another's coat believing it is his own. The act is complete, but the mistake of fact negates the intent to steal; theft fails. If the coat was obviously another's, the mistake is unreasonable and may not excuse.