A more thorough explanation:

But-for cause is a legal term that refers to the necessary element for establishing liability in civil cases and a guilty verdict in criminal cases. It is also known as actual cause.

In civil cases, but-for cause is combined with proximate cause to fulfill the causation requirement of any tort. This means that the plaintiff must prove that the harm they suffered would not have occurred but for the defendant's actions. For example, if a driver runs a red light and hits a pedestrian, the pedestrian can establish but-for cause by showing that they would not have been hit if the driver had stopped at the red light.

In criminal cases, but-for cause is generally sufficient to establish causation. This means that the prosecution must prove that the defendant's actions were the cause of the harm suffered by the victim. For example, if a person shoots someone and the victim dies, the prosecution can establish but-for cause by showing that the victim would not have died but for the defendant's actions.

However, some jurisdictions also allow proving causation through alternative theories. For example, in some cases, the prosecution may argue that the defendant's actions were a substantial factor in causing the harm, even if they were not the sole cause.

It is important to note that once actual cause is established, proximate cause must also be established to return a liable or guilty verdict. Proximate cause refers to the legal concept that limits liability to those harms that are reasonably foreseeable consequences of the defendant's actions.