Introduction to GRE Arguments

There are three key types of short passage questions on the GRE:

1. Weakening or strengthening arguments

2. Identifying structures of arguments

3. Explaining circumstances

Weakening or strengthening arguments

 Studies of individuals suffering from schizophrenia have revealed that such patients are typically missing more than half of the normal levels of a glycoprotein known as “reelin” in a region of the brain.  Because this protein is so commonly deficient in persons suffering from schizophrenia, it seems likely that the absence of the protein is a cause or at least a contributing factor to the disorder, and that its supplementation to the individual would be a viable cure for schizophrenia.

Which of the following would most weaken the argument that reelin deficiency contributes to schizophrenia?

(A) The presence of reelin in the brain can be altered by changes in diet and other behavioral modifications. (B) Reelin deficiency is linked to other disorders such as bipolar personality disorder, the causes of which are thought to be unrelated to schizophrenia. (C) Medicine prescribed to patients with mental illnesses often has the effect of lowering reelin levels. (D) Individuals with more severe cases of schizophrenia typically have lower concentrations of reelin in their brains that individuals with milder cases of schizophrenia. (E) Many individuals with schizophrenia have reelin levels which are perfectly normal for the average human.

An argument can be weakened by attacking its underlying logic - the link between the premise and the conclusion. This argument asserts that reelin deficiency must cause schizophrenia. The reason for this conclusion is because reelin is less common in the brains of individuals with schizophrenia. Answer (C) weakens the argument because it demonstrates that, alternatively, it may be the medicine commonly taken by schizophrenics which reduces the levels of reelin - making the shortage an effect rather than a cause.