_exist_ without form; form cannot _be seen_ without matter. Form is superior to matter, because it needs the latter only to be seen but can exist by itself though not seen; whereas matter cannot _exist_ without form. These two, matter and form, were hidden in God, where they existed potentially until the time came to produce them and realize them _in actu_. Matter is further divided into two kinds. There is pure matter, which enters into the composition of the heavens, and impure matter, forming the substance of terrestrial bodies. Similarly form may be divided at first into two kinds; closed and sealed form, too pure and holy to be combined with matter; and open and penetrable form, which is fit to unite with matter. The pure, self-subsistent form gazes at and illuminates the penetrable form, and helps it to clothe matter with all the forms of which the latter is capable. Now when God determined to realize matter and form _in actu_, he caused the pure form to be clothed with its splendor, which no hyle can touch. This gave rise to angels, seraphim, souls, and all other forms of the upper world. Not all men can see these forms or conceive them in the mind, because they do not unite with anything which the eye can perceive, and the majority of people cannot understand what they cannot perceive with their corporeal senses. Only those who are given to profound scientific investigations can understand the essence of these forms. The light of this pure form then emanated upon the second form, and by the word of God the latter united with the pure matter firmly and permanently, so that there is never a change as long as they are united. This union gave rise to the bodies of the heavens (spheres and fixed stars) which never change their forms. Then the form united with the impure matter, and this gave rise to all the bodies in the sublunar world, which change their forms. These are the four elements, and the products of their composition, including plants.[154] So far we have bodies which do not change their places. Then a light emanated from the self-subsisting form by the order of God, the splendor of which spread upon the heaven, moving from point to point, and caused the material form (_i. e._, the inferior, so-called penetrable form) to change its place. This produced the stars which change their position but not their forms (planets). From this light extending over the heaven emanated another splendor which reached the body with changing form, giving rise to the three species of living beings, aquatic, aerial and terrestial animals, corresponding to the three elements, water, air, earth; as there is no animal life in fire.