**Definition**: A condition without which a result would not happen. **Function**: Tests necessity for outcomes. **Use in law**: Establishes factual causation. **Use in general**: Names what must be present for something else to be possible. **Key test**: Would X still occur if Y were absent? If not, Y is a _conditio sine qua non_. --- **Sources**: - BGHSt 39, 322 (Federal Court of Justice, Germany) - Müller, H.-P. (2020). _Juristische Methodik_ - https://www.wikiwand.com/en/articles/Sine_qua_non