What is the definition of idealism?

from the old testament

• Most of Genesis 1 describes God’s creation of everything before He created humankind. This proves that the emptiness of philosophical idealism. All creation was prior to humankind, so creation is rooted in God, not people.
• God is directly responsible for all reality. As David proclaimed, “The heavens declare the glory of God, and the sky above proclaims his handiwork. Day to day pours out speech, and night to night reveals knowledge” (Psalm 19:1-2).
• The philosophical idealist’s worldview is reminiscent of Satan’s temptation of Eve, claiming her disobedience to God would give her power that belongs only to God: “But the serpent said to the woman, ‘You will not surely die. For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil’” (Genesis 3:4-5).

from the new testament

• Through the apostle Paul, God warns us against vain philosophies: "Don’t let anyone capture you with empty philosophies and high-sounding nonsense that come from human thinking and from the spiritual powers of this world, rather than from Christ" (Colossians 2:8, NLT).
• Those who deny God’s creation are “suppress[ing] the truth” in “unrighteousness” (Romans 1:18). As Paul wrote, God’s “invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse” (Romans 1:20).

implications for today

Idealism encompasses a range of potentially seductive philosophical views about reality, the type of views believers are warned about in Colossians 2:8. Plato hypothesized a realm of unchanging, perfect ideas or "Forms" - such as the concept of a perfect circle or moral perfection - that exist independently of the physical world and serve as the true foundation of reality. According to Plato's view, the physical world is merely a shadow or imperfect reflection of this ideal realm. Later philosophers, such as Berkeley, Hegel, and Kant, have proposed other variants of idealism.

However, rather than follow idealism by presuming that our minds determine what is real, believers can instead align their thoughts with God's truth and reality through immersion in God's Word, prayer and guidance of the Holy Spirit (Romans 12:2).