Vaisesika Sūtra 2.2.20

विध्याविध्यातश्च संशयः ॥२०॥

vidhyāvidhyātaśca saṁśayaḥ ॥20॥

[विध्या (vidhyā): that which shines; अविध्या (avidhyā): that which does not shine; तश्च (taśca): And thereof; संशयः (saṃśayaḥ): Doubt or uncertainty]

Thus, doubt results from those that shine and those that do not shine.