Back in the 1990s, President Bill Clinton famously avoided being found guilty by saying something to the effect of, “it all depends on what your definition of ‘is’ is.” He was widely ridiculed for the statement, but there may be something to it after all. We are going to take a look at the word “is” in philosophy.
First, it should be understood that there are two kinds of “is.” There is the “is” of identity and the “is” of predication. What is identity? That should be easy enough. Without delving into many complex issues, identity is, roughly, A=A. Here are some examples: Imagine you are a first-century Jew seeing Jesus, and you recognize that he fulfills the expectation of the prophet spoken of in Deuteronomy. So you say to your friend, “He is that prophet.” You are here making an identity relationship; you mean to say that these two are not separate individuals but the same person. Other ways include, “Luke, I am your father,” “I am Randy Everist,” “A mountain is a rock,” and so on.
What is predication? In English as well as philosophy, predication of a subject describes something about that subject. It is not the same as identity relationships. For instance, if I say to you, “the basketball player is tall,” I do not mean that there is such a thing as tallness, and the basketball player is it! I mean that the property of tallness can be ascribed to the player. They are descriptions of their subjects. “I am angry,” “It is difficult,” and other such linking verbs with adjectives are all examples of the “is” of predication.
Why is it important to maintain this distinction? First, it holds biblical and theological importance. In 1 John, where the Bible says “God is love,” does it mean, philosophically, that the two are identical? If so, one can say “love is God,” as Augustine famously did. If it is of predication, then does this mean that there can be love independently of God? Is this the same as free will (where free choices are made independently of God, but the fact we can have free will is not)? Some interesting issues are raised.
Second, it can help us avoid misunderstandings on a philosophical and apologetic level. In the moral argument, for example, or in the defense against the Euthyphro dilemma, God is good in the sense of identity. The nature of good is God’s nature, and thus goodness is necessary. Identity and predication may be fascinating to some and boring to others, but they must be differentiated in order to understand properly the philosophical issues.
 Please note this is not to make any kind of political statement or to say that Clinton was correctly applying the principle or not; it’s just a segue into philosophy.