These three aspects of knowledge by analogy are present in St. Thomas’ treatment of God’s goodness. St. Thomas prefaces the discussion with a treatment of goodness in general.¹ The notion of goodness as being insofar as it is appetible must be abstracted from creatures. This treatment is necessary to clarify the meaning of goodness before St. Thomas asks whether goodness belongs to God. That he does clarify goodness from the standpoint of knowledge from creatures, moreover, shows that goodness attributed to God falls under the same general notion of appetible being. This account of goodness is as suitably applied to God as to creatures. Therefore, if we show that God is good, this is not a meaningless phrase, nor a pure equivocation, but actually provides some positive knowledge of God, because both uses of “good” stem from a common principle: being as desired.

St. Thomas proves that goodness belongs to God by comparing effects to their cause. Every thing desires its own perfection. But the perfection of an effect is participation in its cause, since agents make things like themselves. Therefore, the perfection of every agent is desirable by the effect. But God was shown to be the agent cause of all beings.² Therefore, God is appetible, and goodness, as understood in the general account, belongs to Him.

If the same notion of goodness is applied to God as to creatures, how can we understand that this analogy is not identity, that is, that created goodness is not the same as uncreated goodness? The answer lies in the formulation of goodness, desirable being. For since God is not in a genus with any creature,³ being is said equivocally of uncreated and created being. Therefore, although the formulation of goodness is the same in either case, it is applied equivocally to God and creatures. “Good,” however, like “healthy,” is not used purely equivocally, for there is a common principle for using the same word of God and creatures, namely the formulation of goodness explained in Question 5.

Since there is a common principle of using “good,” we can have positive knowledge that God is good. Yet, since this principle is based on a likeness of cause and effect, not an identity, St. Thomas is justified in saying that, “we are not able to consider about God how He is, but rather how He is not.”⁴ For after explaining that the account of goodness we know from created things applies to God in Article I, St. Thomas spends the rest of Question VI explaining that God’s goodness exceeds any creature’s goodness. First, St. Thomas sets the goodness of God apart from all other goods by declaring that God is the highest good.⁵ God was proven to be good by being an agent cause, which necessarily has the perfections of its effects. But God is also not in a genus with created things. Therefore, God is an equivocal cause, so that He has the desirable perfections of His creation in a more excellent way than created things have them. Although the same account of goodness applies to God as to creatures, whatever way a creature is good by having a desirable perfection, God is good in a higher sense by having the same perfection in a more excellent way. Furthermore, St. Thomas goes on to point out that only God has goodness by His essence.⁶ Since His essence is incomprehensible to finite intellects, certainly His goodness is likewise unable to be grasped in itself. He then shows that created goodness emanates from God but is not simply a formal sharing in the one goodness of God,⁷ further clarifying that likeness is not identity. Although God’s goodness is not an entirely empty notion to us because of the similarity to created goodness, the entire treatment has done more to show how created goodness and God’s goodness differ than how they are similar.

The order among analogous uses of a word helps explain the compatibility of knowledge and mystery. St. Thomas has demonstrated that God is good through the similarity of cause and effect. Therefore, since goodness is in God as in a cause, “good” is said primarily of God and secondarily of creatures. But since we came to the general account of goodness through creatures, goodness of creatures is more known to us. In fact, since we have no direct experience of the creator, God’s goodness is not known directly at all. There is no phantasm of God, so the intellect has no object from which to abstract a direct concept of Him. We can know the existence of prime matter through analogy without being able to comprehend it; similarly, we can know some attributes of God without being able to comprehend their full meaning. In both cases there is true knowledge. It is only denied that we can have essential knowledge: not of prime matter because it lacks intelligibility, and not of God because His intelligibility exceeds our way of knowing.