Enter a laboratory: approach the table crowded with an assortment of apparatus, an electric cell, silk-covered copper wire, small cups of Mercury, spools, a mirror mounted on an iron bar; the experimentor is inserting into small openings, the metal ends of ebony-headed pins; the iron bar oscillates, and the mirror attached to it throws a luminous band upon a celluloid scale; the forward-backward motion of this spot enables the physicist to observe the minute oscillations of the iron bar. But ask him what he is doing. Will he answer ‘I am studying the oscillations of an iron bar which carries a mirror?' No, he will say that he is measuring the electrical resistance of the spools. If you are astonished, if you ask him what his words mean, what relation they have with the phenomenon he has been observing and which you have noted at the same time as he will answer that your question requires a long explanation and that you should take a course in electricity .

Thirdly, most of the observations in science made with the help of instruments are constructed or designed in accordance with the specifications provided by some theories. These theories, one may say, constitute the software of these instruments. Belief in the reliability of these instruments implies the acceptance of these theories which have gone into the making of these instruments. Thus, observations presuppose prior theoretical commitments.

Fourthly, observations in science need to be legitimized or ratified by a theory. We all know that Galileo used some telescopic observations to support his theory. His opponents did not consider telescopic observations accurate. It is not that they did not believe in the reliability of telescope. They had no problem in using telescope for terrestrial (of the earth) purposes. They opposed its extension to celestial (of heavenly) sphere where things like background, neighbourhood, possibility of verification which are usually found in normal instances of perception are absent. They rightly demanded from Galileo a theory of optics which would justify the extension of the use of telescope from terrestrial to celestial sphere. Galileo had no such theory. But he rightly believed that in future such a theory could be formulated. Thus, Galileo believed that it was possible to justify the type of observations on which he was dependent. This instance brings out how observations need ratification or justification in terms of either an actual or possible theory. In this sense too, our observations are theory-laden.