Idealism is the account of all things in nature and its experiences as interpreted in the mind. It is the nature of reality as seen through the mind. Things of the external world exist as ideas that exist only in the mind. This is what is said to be metaphysical idealism. It is good to know that idealism has two forms. The one that we are more interested in is metaphysical idealism, while the other type is known as youthful idealism. Youthful idealism is a temporary stage in ones life rather than the idea of life. We will not mention anything about the later type. We should define metaphysics. Metaphysics is the explaining of reality and knowledge through thought, the mind.
Materialism is the opposite of idealism. Materialist views the external objects of the world as purely physical forces. That they exist based on their physical properties, whereas idealist view these objects based on the perception of the mind. The perception based on the idea of "nature", that exists only in the mind.
Idealist views the world as it exists based on the idea or appearances in the minds of the individual soul and the ideas from God. Just as we see in the essay Nature by Emerson. He sees the landscape as beauty in his mind and not the farms and woods that make up the landscape. In the essay of Nature Emerson makes several important points, that we see things from different points of view depending on our position. That our experiences come from some higher mind, that of the mind of God. That the beauty is the truth. That the ideas of religion incorporate the idea of God where ethics does not. Emerson's viewpoint is known as subjective idealism. From Emerson's idea of idealism comes Transcendentalism. The idea that thought comes from the experiences, transcending from the experience. Berkeley mentions this when he speaks of primary and secondary qualities.
George Berkeley another important philosopher held the idea of empiricism that then changed to what he called Subjective Idealism. He held the idea that for the physical world to be real it had to exist in the mind. That this idea would come to us from God and other spirits so as to be perceived in the mind. He believed that things exist based on the person's perception of them. That everything that exists was based on two types of quality. These qualities are categorized as primary and secondary qualities. Primary qualities are those that represent solidity, shape, number, and the like. While secondary represent qualities of color, smell, taste and other qualities of the senses.
Philosophers such Immanuel Kant, G.W.F.Hegel, Fichte, and Schelling held the idea of Absolute Idealism. This is the idea that instead of plurality of the mind, that there is only one mind, one idea, or one experience that comprehends all. They held the idea that the world was part of the mind, which aloud it to be known. This they said was not possible from the idea of realism. That realism would lead to skepticism and doubt. Kant continued his ideas and move to the idea of a transcendental idealism. Kant's idea lead to the fundamentals of ethical and jurisprudential reasoning. That the concepts cannot be arrived at by reason alone, Kant viewed the ideal laws as that which comprises all members of a society to enjoy maximum freedom subjectively, arbitrary to the will of others. Kant felt that the experiences of ideas through the mind are known as phenomena. That the phenomenal world is an expression of power, he would argue that this can not be true without the idea of the noumenal world beyond (noumenal being the idea of not knowing things-in-themselves).
You must also understand that there are many forms of Idealism; Absolute, Transcendentalism, Immaterialism, Subjective idealism, and Representationism. It is also important to mention the ideas of Socrates and Plato, who felt that every philosopher should follow their ideas or arguments to where ever they may lead them. They did believe that these arguments would eventually lead them to some form of Idealism. It seems that there are three approaches to understanding idealism. Through the basic doctrines and principles, it's central questions and answers, and the significant arguments.
Idealism is seen in many from of ideas; literature, paintings, and music.
George Young