How could 1 + 1 + 1 = 1?
A common objection the "Iglesia Ni Cristo" gives to the doctrine of the Trinity is that the doctrine of the Trinity defies simple math and claims 1 + 1 + 1 = 1. Is this a sound argument?
When we examine the doctrine of the Trinity and the use of human language, we see that it is not a valid argument at all, but one that fails to understand the claim made by Trinitarians.
Trinitarians do not believe God is 3 in the same way he is 1.
Trinitarians believe that God is tri-personal, that 3 distinct persons share the one being God. The doctrine of the Trinity does not teach that there are 3 gods. The doctrine of the Trinity teaches that there is only 1 God.
The problem with this "simple math" argument is that it misunderstands the claim of Trinitarians. It assumes Trinitarians teach there are both 3 gods and only 1 God. This is not the case at all. The argument also has a hidden assumption about the nature of God: that God must be unipersonal like the men he created.
We see similar use of language in the Bible concerning a husband and wife.
Mark 10:8 (ESV) - 8 and the two shall become one flesh.' So they are no longer two but one flesh.
We see a husband and wife called both 2 and 1. They are 2 persons, but they are 1 flesh. They are 2 in a different way than they are 1. In the same way, God is 3 in a different way than he is one.
If the INC were to be consistent in how they use this "simple math" argument
then they would need to answer the following question:
1 + 1 = 1?
in relation to the unification of a man and a woman in marriage. Thankfully, the INC is inconsistent on this point and accepst marriage as defined in the Bible. Yet, when the INC rejects the 1 + 1 = 1? argument and accepts the 1 + 1 + 1 = 1? argument, they expose themselves to be ignorant of what the doctrine of the Trinity teaches. Obviously, the Bible is not trying to contradict rules of math. The doctrine of the Trinity does not either.
The INC only makes this "simple math" argument because they do not understand what the doctrine of the Trinity teaches. If one wishes to dispute the doctrine, they must dispute it on its own terms, otherwise they are disputing something that is not the Trinity. Making such an argument is a textbook strawman argument and therefore demonstrates nothing against the Biblical doctrine of the Trinity.
If the INC really wishes to engage in meaningful discussion with Trinitarians and not box as though they are beating the air, it would be wise to invest some time in actually understanding the doctrine of the Trinity.
 This discussion of a husband and wife is not meant to be an analogy for the being of God. It is simply meant to be an exercise in thinking through how the language used in reference to marriage is similar to the language in the biblical doctrine of the trinity.