sbccPhilosophy-111 Critical Thinking And Writing:

Causal Reasoning





Causal Reasoning and Mill’s Scientific Methods

Prior to the Enlightenment of the 18th century, the generally accepted philosophical views of cause and effect evolved from Plato (427-347 BC), through Aristotle (384-322BC), Thomas Aquinas (1224-1274), Rene Descartes (1596-1650), and David Hume (1711-1776). Here are direct citations of each to help understand the evolution of causal reasoning.


"Every¬thing that becomes or changes must do so owing to some cause; for nothing can come to be without a cause." (Timaeus 28a)


“In one sense, then, (1) that out of which a thing comes to be and which persists, is called 'cause', e.g. the bronze of the statue, the silver of the bowl, and the genera of which the bronze and the silver are species.

In another sense (2) the form or the archetype, i.e. the statement of the essence, and its genera, are called 'causes' (e.g. of the octave the relation of 2:1, and generally number), and the parts in the definition.

Again (3) the primary source of the change or coming to rest; e.g. the man who gave advice is a cause, the father is cause of the child, and generally what makes of what is made and what causes change of what is changed.

Again (4) in the sense of end or 'that for the sake of which' a thing is done, e.g. health is the cause of walking about. ('Why is he walking about?' we say. 'To be healthy', and, having said that, we think we have assigned the cause.) The same is true also of all the intermediate steps which are brought about through the action of something else as means towards the end, e.g. reduction of flesh, purging, drugs, or surgical instruments are means towards health. All these things are 'for the sake of' the end, though they differ from one another in that some are activities, others instruments.

This then perhaps exhausts the number of ways in which the term 'cause' is used.”

Thomas Aquinas

"The natural thing necessarily tends to its end in accordance with the power of its form."

"Every agent which acts by natural necessity is determined to one effect," (SCG II: 30.15).

Rene Descartes

“In short, when we are investigating things in the natural world, we should never draw our explanations from the purposes which God or nature had in creating them. We should not be so presumptuous as to think that we are privy to his plans. Instead, we should treat him as the efficient cause of everything. He has endowed us with the natural light, which shows us what conclusions we should draw. Treating him this way, we shall see what we should conclude from those of his attributes which he has willed us to have some knowledge of, to such effects he has brought about which are revealed to our senses. However, we should always bear in mind (as I have already said), that we should trust in this natural light only as long as the contrary has not been revealed by God himself.” (The Principles of Philosophy)

David Hume

“In reality, there is no part of matter, that does ever, by its sensible qualities, discover any power or energy, or give us ground to imagine, that it could produce any thing, or be followed by any other object, which we could denominate its effect. Solidity, extension, motion; these qualities are all complete in themselves, and never point out any other event which may result from them.” (Inquiry Concerning Human Understanding, p.60)

“There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connection....” [pp.61-62]

“When we look about us towards external objects, and consider the operation of causes, we are never able, in a single instance, to discover any power or necessary connection; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other.... Consequently, there is not, in any single, particular instance of cause and effect, any thing which can suggest the idea of power or necessary connection.” [p. 63]

Summary and Critique

Plato simply asserts notion that nothing exists unless it is caused by something else. In doing so, he begs the question.

Aristotle declares that to know something is to know it’s material, efficient, formal and final causes. He too begs the question but his time it’s about the infinite regress of material causes needing a Prime Mover/First Un-Caused Cause.

Aquinas commandeers Aristotle’s teleology (theory of causation) to argue the existence of God as the Prime Mover, First Un-caused Cause, Formal Cause and Final Cause of the Universe, and makes the same fallacies as Aristotle. Descartes doubts that the material world exists at all and therefore we can only be certain that God would not deceive us about the existence of the material world. In that sense God is the efficient cause of all things, since ‘all things’ are ideas in our mind, and God causes all ideas in our mind.

Descartes fails to provide a workable mechanistic model (physics) of exactly how no-material substances ‘causes’ material substance. And at the very beginning of his investigations he equivocates on the meaning of the term ‘existence’.

Hume rejects the claim that propositions about causation are necessary truths because they are beyond what we can discover from experience. We cannot know the truth of propositional claims about particular causes prior to actual experience. First time experience the conjunction we call cause and effect is just that, our first experience of such things. We cannot look at the cause a priori and deduce what the effect will be. Since we know only the conjunction and not the necessary connection between cause and effect, causality is purely a matter of experience a posteriori and not a logically necessary relation. We never experience a ‘cause’ and we never experience an ‘effect’ We merely experience habitual conjunctions in space/time between the phenomenon we call ‘cause’ and the phenomenon we ‘call’ effect.

John Stuart Mill and the Scientific Method

Europe’s 18th century philosophers bequeathed a treasure of intellectual achievements to humanity not seen since the Hellenistic Age of ancient Greece. One of these achievements is well studied by modern students of Philosophy and Science. It is generally referred to as ‘The Scientific Method’ derived from the work of John Stuart Mill (1806-1873).

Often referred to as a ‘radical empiricist’, Mill held the philosophical view that all forms of human knowledge, including logic and mathematics, are inferences we make from sensory experience. Knowledge derived a priori (from reason alone) was an absurd notion to Mill. He therefore set himself to the task of perfecting the only philosophical basis for the only source of human knowing, according to him, sensory experience. For John Stuart Mill, all human knowledge then is derived a posteriori from the senses alone.

When it came to causal reasoning, Mill set down five methodologies describing the inductive process by which we accept the notion that something is the ‘cause’ of something else as the ‘effect’. These five methods have come to form the basis of what is called The Scientific Method in modern academe. Although highly useful for most scientific researchers it is not without important philosophical difficulties and shortcomings.

Mill was careful to present these methodologies merely as grounds for accepting causal relationships that we know by experience in the world around us. He made no metaphysical claims about the existence of ‘causes’ just as he was careful not to make any metaphysical claims about the principles of Logic. All is derived from sense data experience, period!

In our Twenty Distinctions for Critical Thinkers, the difference between necessary and sufficient conditions was defined as:

Necessary / Sufficient Conditions: Any list of required conditions for something to take place is known as list of its necessary conditions. When all of the necessary conditions for something to take place are actually met and the event actually happens that state of affairs is know as the sufficient condition. For example, the moment of ignition is the sufficient condition for the necessary conditions of fuel, oxygen and source of ignition to actually take place.

Seen through the prism of necessary and sufficient conditions then, the five methodological grounds that Mill recommends for the acceptance of any causal argument are as follows.

(where x = the antecedent condition inferred as ‘cause’ and P = the consequent Phenomenon inferred as ‘effect’)

The Method of Agreement: If several instances of a Phenomenon P have only one antecedent condition, X, in common, then X is the cause of P.

Example: Every AIDS case studied by medical researches indicates that the patient absorbed bodily fluids with a person already positive for the HIV virus. Therefore, spread of AIDS is probably caused by this absorption of bodily fluids containing the HIV virus.

In this particular example all AIDS patients studied have only one common condition among them, i.e. that they are known to have exchanged bodily fluids with a person known to be positive for the HIV virus. Thus, this single common factor is justifiably accepted as the ‘cause’ of AIDS in these patients since all AIDS patients have only this factor in agreement. In the Method of Agreement the ‘cause’ is common to all and required for the effect to happen. In this Method absorption of bodily fluids containing HIV is a necessary condition for contracting AIDS. Necessary here means required.

The Method of Difference: If two cases, one in which P occurs, and the other in which P does not occur, have exactly the same antecedent conditions with one exception, namely that X is present in the first but absent in the second, then X is the cause (or a necessary part of the cause) of P.

Example: It’s true that Emily and Scott drank from the same wine bottle at dinner. But only Scott and not Emily had a medically proven seizure reaction to nitrates in food. And since nitrates were found in the wine they consumed at dinner, the nitrates in that wine bottle probably caused Scott to have a seizure after dinner.

Here, the factor that distinguishes Scott from Emily is that Scott had a medically established pre-condition that made him susceptible to seizures whereas Emily had no such pre-condition. Thus, since this medical pre-condition made him different from Emily it is justifiably accepted as the ‘cause’ of Scott’s seizure after dinner. In Method of Difference the ‘cause’ is distinguishing between all. In this Method having such a medical pre-condition is a sufficient cause for Scott’s seizure but not a necessary one since seizures can be induced by many other factors. Sufficient here means enough.

The Joint Method of Agreement and Difference: If several instances in which P occurs have only one antecedent condition, X, in common, while several instances in which P does not occur have nothing in common save the absence of X, then X is the cause (or a necessary part of the cause) of P.

Example: Hillary came down with a rare ailment for which there was no known cure. Aside from the usual childhood illnesses, Hillary had been in good health eating well with moderate but regular exercise. Her doctor administered a new antibiotic to combat her ailment and she made a full recovery. The doctor wanted to determine if Hillary’s recovery was caused by her good eating habits and moderate exercise or caused by the new antibody. Two other cases were found similar to Hillary’s. Researching these other cases the doctor found that one individual did not eat healthy food and never exercised. This patient was also given the new antibody and just as Hillary was this patient made a full recovery. The other case studied involved a patient that had the same healthy diet and exercise regime as Hillary but was not given the new antibiotic. This patient did not recover. Pending more exhaustive clinical trials, the doctor concluded that it was probably the new antibody that cured both Hillary and the other patient.

In this example the new antibody is identified as both the sufficient and the necessary condition for the curative effect in Hillary.

The Method of Residues: If the known effects of antecedent conditions are subtracted from a complex phenomenon P, then the residue of P is caused by the remaining antecedent conditions.

Example: A plant's growth pattern can be analyzed or divided into three parts: the development of large, healthy green leaves, strong stems and root structure, and the production of fruit and flowers. Suppose that we fertilize a test plot with a fertilizer labeled "10-10-10" indicating that it contains equal amounts of nitrogen, phosphorus, and potassium. We know that nitrogen promotes the healthy growth of leaves, and that potassium encourages the development of stronger stems and roots. Our fertilized plants do well in these two categories; they also produce buds and flowers more prolifically than usual. We are justified in inferring that the ‘residue’ increase in the number of buds and flowers was caused by the phosphorus since we already know that the nitrogen and potassium caused the improved growth of leaves, stems, and roots.

The Method of Concomitant Variations: If changes in the magnitude of A and changes in the magnitude of B are always positively associated, or always negatively associated, then either A is the cause of B, or B is the cause of A, or both A and B are the result of a common cause.

Example: When establishing that the acceleration of the planets in their orbits is due to the Sun's gravitational attraction, we cannot turn off the Sun's gravitational field. But we can determine that the velocity of the planets in their elliptical orbits increases as they move closer to the Sun, and decreases as they move further away. Similarly, we might suspect a causal relationship between the average temperature of the Earth's atmosphere and the concentration of ozone in its upper layers since increases in the former seem to be associated with decreases in the latter.


Even Mill’s Methods, useful as they are to confirm or disconfirm scientific causal hypotheses, fail to provide us with the same level of absolutely certain knowledge as valid deductive arguments do. For this reason, competent and conscientious critical thinkers refrain from claiming that their inductive investigations are incontestable and merely make the claim that their hypotheses and conclusions only reflect the ‘best evidence’ available by current research. Probability then is the outcome of induction.