When do you use farthest or furthest?

"Farthest" and "furthest" are both superlative forms of the adjective "far," but they are used in slightly different ways:

Farthest is used when referring to physical distance.

* Example: "The sun is the farthest star from Earth."

* Example: "We hiked to the farthest point of the trail."

Furthest is used when referring to abstract distance, such as time, degree, or extent.

* Example: "This is the furthest I've ever been from home."

* Example: "She went furthest in her efforts to help the community."

* Example: "This is the furthest I've ever gone in learning about this subject."

In summary:

* Farthest is for physical distance.

* Furthest is for abstract distance.

However, in modern usage, "furthest" is often used interchangeably with "farthest" for both physical and abstract distances. This is especially true in casual conversation. So while the distinction exists, you're unlikely to be considered incorrect if you use "furthest" in all cases.