Why do we perceive depth with two eyes?

Answer: Binocular disparity gives depth

Eyes add distances together — Wrong. Eyes don't add distances. Depth perception comes from comparing slightly different images from each eye (stereoscopic vision).

Binocular disparity gives depth ✓ — Correct! Your eyes are spaced apart (~6cm), so each sees a slightly different view of the same scene (binocular disparity). Your brain compares these images—the difference reveals distance. Closer objects have larger disparity. This stereoscopic vision enables 3D perception. One eye still provides depth cues (motion parallax, size, occlusion) but less precise!

Brain guesses from eye angle — Wrong. Brain does use convergence angle (how much eyes turn inward), but the main depth cue is binocular disparity—comparing different retinal images.