People don’t always explicitly state some of the premises while presenting their argument. Knowing these hidden premises gives you the opportunity to spot potential weak points of an argument which would have otherwise gone unnoticed.

In deductive arguments, all premises (ideally) work together to necessitate the conclusion. This means that if we are missing a premise for a deductive argument, then the validity of the argument is dependent on the premise which we are missing. There are two tips that will help you identify a missing premise in a deductive argument:

Tip 1

Extract the argument into standard form and see if there is an obvious gap between the premises and the conclusion.

Take this argument: “Figs are orange because figs are tangerines”

We know that the conclusion of the argument is ‘Figs are orange’ and the argument feels like a deductive argument, but there may be a missing premise. Let’s put this into standard form:

1. Figs are tangerines
2. Thus, Figs are orange

There seems to be a logical leap here and it seems intuitive to say that we need to add another premise to stop this logical leap. It intuitively seems like we should change our extraction to:

1. Figs are tangerines
2. All tangerines are orange
3. Thus, Figs are orange

Tip 2: If you are torn whether a proposition is actually a missing premise for a deductive argument, imagine a world in which all the premises which you know are premises are true but the proposition that you are torn on is false. Is the conclusion necessary?

For example:

1. Figs are tangerines
2. Thus, Figs are orange

If we are trying to figure out if there is a missing premise, we may have a feeling that the missing premise is, ‘all tangerines are orange.” So, to test this, let’s imagine a world where all figs are tangerines, but it is not the case that all tangerines are orange. OK, I can think of a blue tangerine fig, thus the hidden premise must be 2) All tangerines are orange.

How to identify missing premises for inductive arguments:

Identifying missing premises for inductive arguments can be difficult since the premises of an inductive argument do not necessitate the conclusion. Thus, you can’t use the same methods as you would with deductive arguments. But generally, the following method can help you determine what the missing premise is in an inductive argument:

Method: Once you have an idea of what the missing premise of the argument is, imagine a world in which the premises which you know are actually premises are true but the premise in which you are unsure of is not true. In this imagined world, is the conclusion of the inductive argument strong? If not, then that premise is probably a missing premise.

For example: The scientific method engages in hypothesis and empirical reasoning. Thus, the scientific method is probably reliable.

When I see this, I may get a hunch that ‘hypothesis and empirical reasoning are generally reliable’ is a missing premise. So, let’s imagine a world in which that statement is false but the statement ‘the scientific method engages in hypothesis and empirical reasoning’ is true. Is the argument strong? No, it’s not. So, the argument is probably:

1. The scientific method engages in hypothesis and empirical reasoning,
2. Hypothesis and empirical reasoning are generally reliable forms of inference,
3. Thus, the scientific method is probably reliable.

Comprehension Questions

Determine what the missing premises are in the following examples.