Read this: Subjective Idealism (immaterialism or phenomenalism) describes a relationship between experience and the world in which objects are no more than collections or "bundles" of sense data in the perceiver. Proponents include Berkeley, Bishop of Cloyne, an Anglo-Irish philosopher who advanced a theory he called immaterialism, later referred to as "subjective idealism", contending that individuals can only know sensations and ideas of objects directly, not abstractions such as "matter", and that ideas also depend upon being perceived for their very existence - esse est percipi; "to be is to be perceived".
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What is another word for sense data?
unanswerable