Justifications and excuses have developed in various legal systems as defences for wrongful acts. In international law, defences appear in the ILC Articles on State Responsibility, but they conflate justifications and excuses. This article argues in favour of a systematic separation of the two types of defences in international law and applies the typology to the use of force framework. Justifications are legally authorised exceptions to the primary norm. If a prima facie wrongful act can be justified, it is not wrongful. Excuses are defences for acts that are deliberately wrongful but, in the particular circumstances, may be seen as the choice of the lesser evil. The article demonstrates that self-defence under Article 51 UN Charter, Security Council’s authorisation, and intervention by invitation belong to justifications of the use of force. Conversely, humanitarian intervention and perhaps even anticipatory self-defence could be seen as excuses under the defence of necessity. Excuses do not preclude wrongfulness but only mitigate against responsibility for a wrongful act. The use of force that is excused but not justified, therefore, cannot be taken as state practice relevant for an emergence of a customary justification. The excuses/justifications typology preserves the strength of the prohibition of the use of force but acknowledges certain mitigating circumstances where force is used illegally. The article shows that excuses of illegal use of force have been accepted in practice of states and UN organs.