MCAT Critical Analysis and Reasoning Skills Practice Test 3

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Every student of the sciences is taught to be wary of mistaking correlation for causation, but few fully appreciate the difference. Among the first to give an account of this distinction was David Hume (1711–76) in his early masterpiece A Treatise of Human Nature, the composition of which commenced at the prodigious age of 15, when Hume was himself but a student. Though often thought to be surpassed by his treatment of cause and effect in the more mature An Enquiry Concerning Human Understanding, the discussion in the Treatise is remarkable for situating causation squarely within the context of human psychology.

Hume's analysis begins from a simple principle, "that all our ideas are copy'd from our impressions," by which he means that all knowledge ultimately derives from sense experience—an axiom he shares with fellow empiricists Locke and Berkeley. Causation is no different, and thus Hume sets out to determine the original impressions (today more commonly called perceptions or sensations) whence this idea derives. According to his analysis, causation is nothing that is intrinsic to any particular object but rather only emerges in the relations between two objects, namely, a cause and an effect. He notes three specific relations that are "essential" to the idea of causation: contiguity (spatial proximity), temporal priority of cause before effect, and an additional "necessary connexion" between the two. This last is what distinguishes causation from mere coincidence, so Hume devotes several sections to uncovering what it is.

His conclusion may shock those unaccustomed to skeptical thinking. Hume argues that this necessary connection that makes one entity the cause of another is purely a creation of the mind: "necessity is nothing but that determination of the thought to pass from causes to effects and from effects to causes, according to their experienc'd union." Such behavior is the product of custom, a mental habit established after we repeatedly perceive similar sequences of cause and effect, such as when a moving billiard ball transfers momentum to a resting one after they collide—one of parlor gamesman Hume's favorite examples. Logic does not dictate that momentum should be transferred in a collision, for we could easily imagine one ball colliding into another and producing any number of other results; only experience shows us it is so.

Hume's inquiries lead him to formulate the following definition: "A cause is an object precedent and contiguous to another, and so united with it, that the idea of the one determines the mind to form the idea of the other, and the impression of the one to form a more lively idea of the other." He can remain confident that this determination of the mind is a customary connection, not a logical one, with his astute observation that all causal reasoning presupposes "that the future resembles the past," a claim which need not be true. In fact, such a claim could only ever be taken on faith—for how could it be proved? If one were to argue that, in the past, what would become the future at that point has always turned out to resemble the prior past, so we can expect the same in the future, one would be begging the question. How do we know the laws of nature won't change tomorrow?

If Hume is right, there is naught but the quirks of the psyche that properly distinguishes causation from what he designates "constant conjunction" (correlation). Later thinkers would come to call this the "problem of induction," for it demonstrates how all inductive reasoning—which moves from particular pieces of evidence to a universal conclusion—is ultimately uncertain.

1. Which of the following statements is assumed without support in paragraph 3?

  • A. Hume says that the necessary connection between cause and effect is simply a mental custom.
  • B. Momentum is transferred if an object in motion collides with an object at rest.
  • C. The mind infers a necessary connection after experiencing one instance of a cause and its effect.
  • D. The truth of a claim is not logically determined if it can be imagined otherwise.

2. According to the discussion in the final paragraph, one example of "inductive reasoning" would be concluding that an automobile tire will never go flat on the basis of:

  • A. repeated daily observations of the tire staying intact.
  • B. the logical necessity of all tires being incapable of going flat.
  • C. a customary habit of jumping to faulty conclusions.
  • D. knowledge that the tire is made of an indestructible material.

3. Based on the passage, what best explains how "all causal reasoning presupposes 'that the future resembles the past'" (paragraph 4)?

  • A. Reasoning about causality is ultimately founded on an assumption established by custom rather than by logic.
  • B. The laws of nature must be unchanging from past to future.
  • C. It is not necessarily the case that the past and future resemble one another.
  • D. Past conjunctions of cause and effect would yield no causal knowledge if the future operated by new laws of nature.

4. The claim "causation is nothing that is intrinsic to any particular object" most nearly means that objects:

  • A. can never be adequately comprehended by the human mind.
  • B. are by nature effects rather than causes.
  • C. can be understood as causes only relative to other entities.
  • D. cannot be the cause of other objects.

5. Which of the following, if true, would most UNDERMINE Hume's conclusions about cause and effect?

  • A. There is no reason to believe that the laws of nature will change tomorrow.
  • B. Some knowledge is attainable completely independent of experience.
  • C. Most students of science fully appreciate the difference between correlation and causation.
  • D. Claims about causal relations can always be doubted.