In addition to multisensory coherence and the testimony of other people, there is a third reason for inferring that our perceptions of objects are approximately true: we can often corroborate them with measurements taken by instruments. People don't usually subject a loaf of bread to instrumental inspection, but a physicist could use calipers to measure its height and width, a spectrometer to measure the color reflectance of the loaf, an artificial odor detector to measure molecules near the loaf, and so on. Such measurements carried out by people or possibly even by robots provide further
evidence best explained by the supposition that the loaf of bread exists. Similar arguments support inference to the existence of many other kinds of objects, from lions to mountains. Contrary to empiricism, scientific knowledge does not come just from our senses, but goes beyond them via a multitude of reliable instruments from telescopes and microscopes to Geiger counters (used to measure radiation) and particle colliders (used to detect the behavior of subatomic particles). The efficacy of scientific instruments is incompatible with idealism, because their measurements do not depend on mental activity, but it fits well with constructive realism.