IMAT 2015 Q7 [Assumption | Dental Health]

Studies are taking place to assess the benefits to dental health of adding fluoride to drinking water, a process known as mass medication. The Health Minister has urged consideration of fluoridation, particularly in deprived areas where dental care is poor. Fluoride can occur naturally in the water because of fluoride containing minerals. Fluoride, if in the water, improves dental health by up to 50 percent. Even so, fluoridation should not take place. A campaign leader opposed to fluoridation has spoken of her experiences of living in a fluoridated area of the USA. She experienced feelings of apathy and depression; her 2 year old son showed autistic tendencies and had white flecks on his teeth. These symptoms disappeared when they returned home from the USA.

Which one of the following is an underlying assumption of the argument above?

A. Mass medication is always wrong.

B. Fluoridation of water is a person’s only source of fluoride.

C. The reported health symptoms were caused by fluoride in the water.

D. Fluoridation is cheaper than improving dental facilities.

E. Fluoridation is only necessary in deprived areas.


  1. Identify the question type. Although not phrased in the typical Cambridge format (“What is the assumption in the argument…”) we can easily identify that it is asking for an assumption.

  2. Strategy Tool Kit for solving assumptions

  3. Find the conclusions

  4. Find the reasons

  5. Find the unwritten link that the conclusion relies on

  6. Discard and decide (use negation test if needed)

This question should be a quick solution if you are familiar with these kinds of problems.

What should we be looking out for?
The lack of linkage between the arguments made by the author and the problem itself. What do I mean by this? Notice how the author has talked about how the campaign leader has had symptoms without any ties to fluorine. There is no conclusive evidence that links these illnesses and the fluorine in the water, if we do not assume that they are linked then the argument is completely invalid. The argument is already weak because of how speculative it is, so we can easily tell that the assumption has to be that there is a connection between the woman’s symptoms and the water. Now for the answers:

A Mass medication is always wrong.

This is not relevant in our case. It is an assumption, but it is way too generalized and it cannot be definitely taken from this text. It is not related to the opinion of the author, which is that we should stop the fluorination of the water. There is also no mention of other mass medication, and there may be benefits in other circumstances that the author agrees with. Therefore A is incorrect.

B Fluoridation of water is a person’s only source of fluoride.

This is not important to the author’s argument, and if anything it might weaken the argument. A missing piece of information not given in the text is whether or not fluorine is needed/necessary in our diets, but if this was the case, then the fluorination of water would be important in order for us to ensure we are intaking the correct amounts. Therefore B is incorrect because it is not needed to be assumed for the argument to be valid, and if anything it weakens the argument.

C The reported health symptoms were caused by fluoride in the water.

This is what was mentioned in the introduction before going into the answers. Without this key piece of information, there is no link between the health symptoms and fluoride in the water so the author cannot use fluoride’s impact on health as a reason to argue it should be banned from being added to the water supply. Therefore C is correct.

D Fluoridation is cheaper than improving dental facilities.

If there are truly other health symptoms, then this would not be a relevant argument because it is causing more harm than good. These medical problems that arise could require treatment worth more than dental facilities, therefore it would not matter if it was cheaper because it would cost more in the future. Regardless, price is not really of importance in the argument, it was only mentioned as the reason why it is typically done. Therefore D is incorrect.

E Fluoridation is only necessary in deprived areas.

We cannot assume this based on what is given to us in the argument and it is not needed in order for the argument to be valid. The text fluorination is needed “particularly in deprived areas…” but this does not rule out its use in other areas. Regardless, this would weaken the argument of the author because it would mean it is not as big of a problem as it would be if it was nationally. Therefore E is incorrect as it is not needed for the author’s argument to stand.