Subjective idealism is a theory in the philosophy of perception. It describes a relationship between human experience of the external world, and that world itself, in which objects are nothing more than collections (or bundles) of sense data in those who perceive them.
A famous proponent of subjective idealism was 18th century Irish philosopher George Berkeley.
This theory has much in common with phenomenalism, the view that physical objects, properties, events, etc. (whatever is physical) are reducible to mental objects, properties, events, etc. Thus reality is ultimately made up of only mental objects, properties, events, etc.
The foundations of idealism in the modern sense were laid by the thinkers who sought breathing room for mind and will in a deeper analysis of the relations of the subject to the world that it knows.
The conflict of idealism with these two lines of criticism - the accusation of subjectivism on the one side of intellectualism and rigid objectivism on the other - may be said to have constituted the history of Anglo-Saxon philosophy during the first decade of the 20th century.
These on their side, to be subject in the true sense must be conceived of as possessing a life which is truly their own, the expression of their own nature as self-determinant.
IDEALISM[idealism] the attitude that places special value on ideas and ideals as products of the mind, in comparison with the world as perceived through the senses.
In modern times idealism has largely come to refer the source of ideas to man's consciousness, whereas in the earlier period ideas were assigned a reality outside and independent of man's existence.
The post-Kantian German idealism of J. Fichte and Friedrich von Schelling, which culminated in the absolute or objective idealism of G. Hegel, began with a denial of the unknowable thing-in-itself, thereby enabling these philosophers to treat all reality as the creation of mind or spirit.