When deluded thoughts grasp at sense objects, the marks of form appear

Original text of the Laṅkāvatāra Sūtra: 其余诸识。有生有灭意意识等。念念有七。因不实妄想。取诸境界。种种形处。计著名相。不觉自心所现色相。不觉苦乐。不至解脱。名相诸缠。贪生生贪。

Explanation: Apart from the self-natured pure mind of tathāgatagarbha, all the rest are the mind, manas, mind consciousness, and so forth, which arise and cease. In every thought-moment, sentient beings manifest the seven consciousnesses, displaying their impermanent nature of arising, ceasing, and change. Because they do not know the true reality of the dharma realm, they give rise to insubstantial delusive thoughts, grasping at sense objects as real, grasping at the various forms and appearances of the six sense objects, and then attaching names and labels to them. They do not know that all these objects and appearances are illusory manifestations of the self-natured pure mind. Due to this ignorance, they fail to awaken to the suffering and pleasure brought by attachment to objects; with suffering and pleasure, liberation cannot be attained. Since beginningless kalpas, sentient beings have been entangled by worldly names and labels, giving rise to all kinds of craving and afflictions.