The basic law and natural dynamic of the mind whereby ideas in the mind are expressed outward (though without leaving the mind), thus causing effects after their nature and likeness. The mind then looks upon and experiences these effects. Through this process of causing effects, the mind's original ideas are reinforced, completed and increased. In short, the mind's thoughts become its expression and this expression becomes its experience. 1. In Heaven, God extended His Will, His Love, to create His Son, the Christ (see creation). 2. In Heaven, our function is also to extend. 3. On earth we extend or project our thoughts outward. The result is that what we think becomes what we perceive and what we perceive becomes what we believe (see "projection makes perception"). 4. Our function on earth is to extend love, forgiveness and healing to others. Merely perceiving others as forgiven is an extension to them, yet we may also use our body to actively communicate this forgiveness. Through healing them, our own healing becomes reinforced (see giving/receiving, savior and witness). 5. Under the ego, extension is distorted and takes the form of projection. Because of this distortion, we do not see the connection between the thoughts in our minds and what we see without. Extension is the umbrella for many of the Course's ideas. See cause and effect, communication, creations, "ideas leave not their source", laws, making, miracle, special function, teaching, will.