Is Consciousness-Only the Same as Idealism?

No. Although Consciousness-only doctrine emphasizes mind, it does not deny the existence of either matter or objective phenomena. If these were negated, then everything should be negated, including consciousness, and there would be no consciousness to emphasize. In fact, philosophical idealism can be interpreted to encompass almost everything except materialism. For example, George Berkeley (1685–1753) can be considered a subjective idealist. Georg Hegel (1770–1831) may be regarded as an objective idealist, and Arthur Schopenhauer (1788–1860) a volitional idealist. William James (1842–1910) may be considered an empirical idealist, and Henri-Louis Bergson (1859–1941) an intuitive idealist. And Bertrand Russell (1872–1970) can be classified as a skeptical idealist.  
 
In brief, any form of idealism will require the specification of some normative standard to serve as the basis for its theories. Once they select some adored criterion or ideal, philosophers inevitably make the mistake of over-generalizing from a partial truth. The skeptical idealists are more open-minded, but they cannot provide an ultimate answer for guidance, leaving people feeling anxious and paralyzed. The Consciousness-only school of Buddhism does say that “the three realms are merely consciousness,” meaning all phenomena within the three realms are manifested by the eighth consciousness. That is to say, all physical phenomena, everything in the non-sentient world (qijie), are the objective aspect (xiangfen), or active dharmas, of the eighth consciousness. The theory does not, however, deny the existence of sentient beings outside the individual self.
 
The claim that “the three realms are merely consciousness” only says that all phenomena within the three realms are jointly produced by the eighth consciousnesses of all sentient beings within the three realms; that is, phenomena are produced by sentient beings’ collective karma. The eighth consciousness mentioned here comprises not just the present mind, but is also that consciousness perfumed from beginningless time by karmic forces. From the active dharmas of karma-conditioned consciousness are formed the objective aspect of the eighth consciousness, the phenomena of the three realms, and the world in which we live.
 
Matter in our world is formed by the joint activities of each eighth consciousness of the sentient beings in our world. Likewise, sentient beings and their interactions are manifestations of the eighth consciousnesses of all the sentient beings in the same world.
 
The cosmology of the Consciousness-only school can be described as “conditioned arising from the ālaya-vijñāna” (laiye yuanqi). Ālayavijñāna is Sanskrit for “eighth consciousness” and means “storehouse consciousness.” It stores all karmic seeds [karmic impressions]. Considering things from a noumenal [benti, “fundamental embodiment or substance”] perspective, when karmic seeds become active they bring about karmic recompense; hence, we can say that everything is produced by consciousness. When viewed from the phenomenal (xianxiang) perspective, we can describe the process as “conditioned arising induced by karma,” because the karmic recompense (i.e., the phenomena) produced by the eighth consciousness results from the individual’s karma.
 
From a methodological viewpoint, both “conditioned arising from the ālaya-vijñāna” and “conditioned arising induced by karma” are in accordance with the principle of conditioned arising, which claims that phenomena come into existence only via the combination of multiple conditions. Accordingly, conditioned arising is the basic truth of Buddhism. The ultimate goal of Buddhist [inquiry] is [to understand or realize] emptiness. Because it is unnecessary to posit any metaphysical object of adoration, Buddhism does not fall into the quagmire of over-generalizing from partial truths. And because conditioned arising implies emptiness of nature—emptiness of both the self and dharmas—people are not left feeling anxious, rudderless, and paralyzed.
 
Most philosophers cannot realize the emptiness of self, not to mention the emptiness of dharmas (metaphysical standards or ideals which are adored). If they were to see the emptiness of the philosophical bases to which their egos cling, they would lose the foundation for their ideas and become lost, wandering souls. Therefore, philosophical idealism cannot measure up to the Buddhist doctrines of Consciousness-only.