 The Scholastic concept of essence, or what is more properly called a ‘substantial form’, is of an imperceptible, immaterial essence that imposes order onto the matter that it is joined with and makes it a member of a natural species or genus, imbuing it with all of its relevant characteristics, i.e., its essential properties. Essential properties are those features that tell us to what species or genus an object belongs, e.g., being warm blooded is an essential property of mammals, being rational is an essential property of humans, being yellowish and heavy are essential properties of gold. Each of these essential properties is caused by the substantial form that is conjoined with the matter of the substance to make it what it is.