This article is the first of a series of articles in which we learn all that is there to learn about the basics of CR causal arguments on the GMAT. Thus, we will look at the following in detail:

1. What is causality?
2. What is a causal argument?
3. State the assumptions behind a causal argument.
4. What are the ways of strengthening causal arguments?
5. Solving an official strengthen question.

## What is causality?

In GMAT CR, the stimulus often contains a cause and effect relationship. Such a relationship clearly states that a certain event A caused a certain event B. Thus, event A is the cause and event B is the effect of that cause. For example:

The unusually low amount of rainfall this year caused/led to/ resulted in low production of corn.

In the above:

EVENT A = CAUSE: unusually low amount of rainfall this year

EVENT B = EFFECT: low production of corn.

Let’s look at another example:

The increased levels of air pollution are due to an increase in the number of vehicles being driven on the road.

CAUSE: increase in the number of vehicles being driven on the road.

EFFECT: increased levels of air pollution

Let’s now look at where exactly such causalities are mentioned in an argument.

## What is a causal argument?

We know that an argument is made up of the premise/s and the conclusion. Thus, a causal relationship may be a part of the premise or the conclusion – that is, a cause and its effect may be stated as a premise or maybe a part of the conclusion. Let us look at the following two arguments:

Argument 1:

Exhaust from the vehicles driven on the roads causes air pollution. Therefore, air pollution can be reduced by reducing the number of vehicles being driven on the roads every day.

In this argument, statement 1 is the premise which talks about two events that display a cause-effect relationship. The conclusion contains a recommendation based on that relationship. Thus, causality is a part of the premise.

Argument 2:

The number of vehicles being driven on the roads has increased in the last one year along with an increase in air pollution levels. Thus, the exhaust from the vehicles must have led to the increase in pollution levels.

In this argument, statement 1 is the premise which talks about two events which happened around the same time. The conclusion draws a cause and effect relationship between those two events. Thus, the causality is present in the conclusion.

NOTE: Since the crux of the argument lies in the conclusion, a causal argument is one in which the causality is stated in the conclusion. Henceforth, whenever we talk about a causal argument, we are referring to one in which causality is present in the conclusion. If the causality is present only as the premise, it is not to be treated as a causal argument.

Now that we have understood the idea of causality and causal argument, let us delve deeper into the assumptions behind a causal argument.

## The assumptions in a causal argument

Like all CR arguments, a causal argument also contains certain assumptions. The good thing about causal arguments is that these assumptions are pretty much same for all causal arguments. On the other hand, in other CR arguments, the assumptions depend on the given scenario. Let’s delve deeper into the earlier example to understand these central assumptions in a causal argument:

Example:

The number of vehicles being driven on the roads has increased in the last one year along with an increase in air pollution levels. Thus, the exhaust from the vehicles must have led to the increase in pollution levels.

The premise talks about two events that took place around the same time- in the last year.

Event A: The number of vehicles being driven on the roads increased

Event B: The air pollution levels increased.

However, the premise does not tell us that a cause – effect relationship exists between the two events. The author draws that relationship between the two events in the conclusion, making this argument a causal argument.

Now, what are the assumptions that the author makes while drawing a cause and effect relationship between the two events?

Assumption #1: The author assumes a certain sequence between the two events. The author assumes that event A must have happened before event B.

Thus, first the number of vehicles being driven on the roads increased

Thereafter the air pollution levels increased.

Assumption #2: The author assumes that nothing other than event A caused event B. In other words there is “no alternate cause” that caused event B

Thus, the increase in pollution levels did not take place  because of any reason other than the increase in the number of vehicles driven on the roads.

Assumption #3: The author assumes that event B did not cause event A. In other words, there is no reverse causality – the effect did not cause the “cause”.

If we negate any one of the assumptions above, the causality, in conclusion, will not hold.

1. If the air pollution levels were already increasing before the number of vehicles driven on the roads increased, then the cause-effect relation will cease to exist.
2. Suppose something else caused the increase in air pollution levels. In that case, the author cannot confidently say that it was an increase in the number of vehicles being driven on the roads that led to the rise in pollution levels.
3. However illogical it may sound, if the increased pollution levels were responsible for the increase in number of vehicles being driven on roads, then the author cannot draw the causal relationship.

In GMAT CR, very few assumption questions are based on causal argument. Most causal arguments appear in strengthen, weaken or evaluate questions. In such cases, the correct answer choices are built along the lines of the above three central assumptions. However, there are some more ways of strengthening/weakening a causal argument. Let’s look at ways of strengthening them. We will look at ways of weakening a causal argument, which is one of the basics of causal arguments on the GMAT CR in the next article of this series.

## Ways of strengthening causal arguments

We have already seen the three assumptions in action.

We build strengtheners along the lines of these assumptions. Other than the assumption, any evidence of these three assumptions can also help strengthen the causal argument. Let us use the previous example to see how the following can be strengtheners on a causal argument:

Example:

The number of vehicles driven on the roads increased last year, causing increased air pollution levels. Thus, the exhaust from the vehicles must have led to the increase in pollution levels

Given that

the cause is X: exhaust from the vehicles

and the effect is Y: increase in pollution levels

1. No alternate causes (Z) for stated effect – Z did not cause Y
1. Any choice that eliminates an alternate cause will automatically act as a strengthener.
1. In the last year, there was no significant increase in the number of manufacturing industries which are another major cause of air pollution.
2. If cause occurs, then effect occurs – If X, then Y
1. Any choice that shows that whenever the cause occurs, the effect also occurs will strengthen the argument.
1. Twice in the past, the air pollution levels increased to unprecedented levels immediately following sudden increases in vehicular traffic.
3. No cause, no effect – No X, no Y
1. A choice that indicates that in the absence of the cause, the effect was also absent, will be a strengthener.
1. Areas with lowest number of vehicles driven on roads have lowest levels of air pollution.
4. No possibility of reverse relationship – Y did not cause X
1. A choice that shows that Y could not have caused X will work as a strengthener.
1. Air pollution levels were significantly lower prior to the increase in the number of vehicles driven on the roads.
5. Show data used are accurate or eliminate the possibility of problems with data
1. Any choice that provides evidence to show the above will strengthen the conclusion.

Suggested Read: GMAT Verbal CR – Strengthen Practice Question #1

## Solving an official strengthen question

In response to viral infection, the immune systems of mice typically produce antibodies that destroy the virus by binding to proteins on its surface. Mice infected with the herpes virus generally develop keratitis, a degenerative disease affecting part of the eye. Since proteins on the surface of cells in this part of the eye closely resemble those on the herpes virus surface, scientists hypothesize that antibodies cause these keratitis cases to the herpes virus.

Which of the following, if true, most helps to support the scientists’ reasoning?

(A) Other types of virus have surface proteins that closely resemble proteins found in various organs of mice.

(B) Mice infected with only the herpes virus produce as many antibodies as infected mice develop keratitis.

(C) Mice infected with a new strain of the herpes virus that has different surface proteins did not develop keratitis.

(D) Mice not infected with the herpes virus can sometimes develop keratitis.

(E) There are mice that are unable to form antibodies in response to herpes infections, and these mice contract herpes at roughly the same rate as other mice.

STEP 1- ANALYZING the STIMULUS

Given:

• In mice, viral infection causes immune system to produce antibodies.
• These antibodies bind to the surface proteins of virus and destroy the virus.
• Mice with herpesvirus develop keratitis in eye
• The proteins on these eye cells resemble herpesvirus proteins
• Conclusion: In such cases, herpes virus antibodies cause keratitis

STEP 2- PRE-THINKING

1. From the argument, we can infer that the herpes virus antibodies probably bind to the proteins on the eye cells since these proteins look like the herpes virus proteins. This is how keratitis forms in the eye.
2. We have  a causal argument since the conclusion contains a cause-effect relationship:
Cause: Antibodies to the herpesvirus bind to the proteins on the eye cells (because of the similarity between the virus proteins and the eye proteins)

Effect: Keratitis in the eye

• Now when we are looking at the answer choices, we should look out for the following:
• Z did not cause Y
• If X, then Y
• No X, no Y
• Y did not cause X

### STEP 3- ANSWER CHOICE ELIMINATION

A. Other types of virus have surface proteins that closely resemble proteins found in various organs of mice.

(Other types of virus and proteins found in other organs are not at issue here. This choice is out of scope.

Incorrect Choice)

B. Mice infected with the herpes virus don’t develop keratitis and produce as many antibodies as infected mice that develop the disease.

(This choice talks about mice infected by herpes virus but not suffering from keratitis. So, here the cause (herpesvirus antibodies) is present but the effect is not. This choice says the cause is present but there is no effect. This choice is more of a weakener.

Incorrect Choice)

C. Mice infected with a new strain of the herpes virus that has different surface proteins did not develop keratitis.

(New herpesvirus has different surface proteins. In this case, the proteins in the eye cells will no longer be similar to the new herpesvirus surface proteins. And thus, in the absence of similarity, antibodies will not bind to the surface of the eye cells and there will be no keratitis in the eye. This choice fulfils the criteria – No cause, no effect – No X, No Y. This strengthens the causality in the conclusion.

Correct Choice.)

(D) Mice not infected with the herpes virus can sometimes develop keratitis.

(Per this choice, something else caused keratitis). These are not the cases at issue here. The argument is talking about cases where herpes virus and keratitis developed in the mice simultaneously. This is out of scope.

Incorrect Choice.

(E) There are mice that are unable to form antibodies in response to herpes infections, and these mice contract herpes at roughly the same rate as other mice.

(per this choice, the cause, the antibodies, and the effect, keratitis, both are absent. Such cases are not a part of the issue at hand.

Incorrect Choice)

Suggested Read: How to score 700+ on the GMAT