Using Logic in Apologetics

by Mark Farnham

In a previous post we introduced the basics of logic. Here we see how logic is used in apologetics encounters.

When we apply the science of arguments to apologetics, it is clear that the arguments used against Christianity are often stated informally. The informal statement “I don’t believe in God because I can’t see him” can be written into a formal syllogism such as:

P1: I must see something to believe in it.

P2: I don’t see God.

Conclusion: Therefore, I don’t believe in God.

Notice that Premise 1 (P1) is not stated explicitly in the informal statement, but it is implied. This is where questions are so important in conversations about the gospel. I would not know the reason for someone’s rejection of God unless I asked. Once someone tells me they don’t believe in God because they feel they must see something to believe it, I am able to construct the syllogism above. I can now see his argument clearly and can address it.

In this case the informal statement, “I don’t believe in God because I can’t see him” is an incomplete syllogism. When a syllogism is incomplete, it is called an enthymeme. The challenge of identifying logical problems in an argument is the difficulty of taking the enthymeme as it is stated and filling in the missing terms, so the complete syllogism is clear. This takes time and practice, but eventually you will begin to be able to identify the unstated assumptions of a conversation partner (or yourself!).

In fact, a number of additional premises could be inferred from such a statement, depending on the context of the conversation. For example…

Using Logic in Apologetics