In philosophy, idealism is the group of philosophies which assert that reality, or reality as we can know it, is fundamentally mental, mentally constructed, or otherwise immaterial. Epistemologically, idealism manifests as a skepticism about the possibility of knowing any mind-independent thing. In a sociological sense, idealism emphasizes how human ideas—especially beliefs and values—shape society. As an ontological doctrine, idealism goes further, asserting that all entities are composed of mind or spirit. Idealism thus rejects physicalist and dualist theories that fail to ascribe priority to the mind. 

The earliest extant arguments that the world of experience is grounded in the mental derive from India and Greece. The Hindu idealists in India and the Greek Neoplatonists gave panentheistic arguments for an all-pervading consciousness as the ground or true nature of reality. In contrast, the Yogācāra school, which arose within Mahayana Buddhism in India in the 4th century CE, based its "mind-only" idealism to a greater extent on phenomenological analyses of personal experience. This turn toward the subjective anticipated empiricists such as George Berkeley, who revived idealism in 18th-century Europe by employing skeptical arguments against materialism.
what does Idealism reject?
ontologically what does it assert?
where did the earliest arguments that experience is mental come from?
how does idealism manifest Epistemologically?
about what exactly?
where did the Yogācāra school come from?
who was an empiricists
when did he revive idealism in Europe?
what is idealism a group of?
does idealism shape society?
who gave panentheistic arguments for consciousness?
physicalist and dualist theories
Idealism thus rejects physicalist and dualist theories
that all entities are composed of mind or spirit
that all entities are composed of mind or spirit
India and Greece
The earliest extant arguments that the world of experience is grounded in the mental derive from India and Greece
as a skepticism
 Epistemologically, idealism manifests as a skepticism
about the possibility of knowing any mind-independent thing
about the possibility of knowing any mind-independent thing
within Mahayana Buddhism in India
 the Yogācāra school, which arose within Mahayana Buddhism in India
George Berkeley
empiricists such as George Berkeley
18th-century
George Berkeley, who revived idealism in 18th-century Europe
philosophies
 idealism is the group of philosophies
yes
idealism emphasizes how human ideas—especially beliefs and values—shape society.
The Hindu idealists in India and the Greek Neoplatonists
The Hindu idealists in India and the Greek Neoplatonists gave panentheistic arguments for an all-pervading consciousness