Causal Explanation Review Cause something which brings about or increases the likelihood of an effect Correlations point to and give evidence of causal relations but do not themselves demonstrate causation Correlation is symmetrical Causation is directional Differentiate variables Independent variable possible cause what is manipulated Dependent variable possible effect depends on the independent variable Review 2 Strongest evidence for causation comes from experiments Manipulate the independent variable and detect effect on the dependent variable Speak of manipulated independent variable When manipulation is not possible Measured independent variable In either case the dependent variable is measured 1 Review 3 Testing causing claims Often requires operationalizing the variable or developing measures in terms of which we can secure data To confirm a causal hypothesis Identify a prediction that would not be true if the causal hypothesis were not true If the prediction is true reason by modus tollens to the truth of the hypothesis To falsify a causal hypothesis Identify a prediction that would be true were the hypothesis true If the prediction is not true reason by modus tollens to the falsity of the hypothesis Seeing Causes A tradition in philosophy whose roots lie with David Hume maintains that we never see causation only events preceding other events But some visual displays such as those developed by Albert Michotte are hard to see in any other way Describe what you see 2 What is a cause A variable some of whose values bring about or increase the value of the effect variable Two more specific notions of cause The cause is sufficient to bring about the effect The cause is necessary to bring about the effect Neither works perfectly but each is suggestive of important features of causation and help us understand how to test causal claims Recall the Logic of Necessary and Sufficient Conditions Conditional relations between statements captured with the connnective if then If the score is tied then we will play another round The score being tied is sufficient for playing another round Playing another round is necessary when the score is tied Better captured by Only if we played another round was the score tied We can extend the notions of necessary and sufficient to causes Sufficient causes Examples of factors sufficient to bring about an effect Dead battery is sufficient for car not starting Placing water in a normally operating freezer is sufficient for it freezing Ingesting enough hemlock is sufficient for dying Increased exercise without eating more is sufficient for weight loss 3 The value of sufficient causes A sufficient cause gives us a recipe for producing an effect we want If you don t want someone to drive your car totally run down the battery If you want to loose weight exercise Whenever I get the urge to exercise I lie down until the feeling passes away Robert M Hutchins former President of the University of Chicago I have never taken any exercise except for sleeping and resting and I never intend to take any Exercise is loathsome Mark Twain Essays Seventieth Birthday The difficulty with sufficient causes For many conditions in which you think you have found a sufficient cause an exception can be found If you take an antidote with your hemlock should one be found you might escape death If you put salt in the water it may not freeze even when temperature is less than 32o F The difficulty with sufficient causes Few factors we identify as causes are really sufficient to bring about their effect They suffice only in the context of background conditions that are assumed to be in place Turning the ignition switch will start the car only if it is hooked up to the rest of the ignition system there is an engine in the car there is gas oxygen is available Often need to specify a conjunction of factors to arrive at a sufficient cause and it is very difficult to note all of them 4 Necessary causes Something that is necessary to produce an effect Sex is necessary for producing babies Oxygen is necessary for combustion Herpes zoster is a necessary cause of chickenpox Early exposure to language is necessary for normal language development For want of For want of a nail the shoe was lost For want of the shoe the horse was lost For want of the horse the rider was lost For want of the rider the battle was lost For want of the battle the kingdom was lost And all for the want of a horseshoe nail The value of necessary causes Provide a way of preventing something Avoiding sex does prevent babies and AIDs Eliminating oxygen does stop fires Not having Herpes zoster in you prevents chickenbox 5 The difficulty with necessary causes For many supposed necessary causes there are alternatives Sex is not strictly necessary for producing babies in vitro fertilization can replace it Recap Quick description Value of identifying Inadequacy as a full characterization of cause Practical difficulties Sufficient Causes A sufficient cause can bring about an effect e g ordinarily pulling a trigger of a loaded gun suffices to fire a gun If we know sufficient causes we can be empowered to bring about desired effects e g if we know how to fire the gun we can Events which we may want to call causes aren t strictly speaking sufficient since we can imagine contexts in which the causes fail to suffice e g pulling a trigger fires a gun but not if the bullets are duds Sufficient conditions are difficult to identify and perhaps impossible to perfectly specify since such a specification would require an exhaustive description of the relevant background conditions Necessary Causes A necessary cause is a precondition that must obtain for the effect to manifest e g guns need a hammer to fire If we know necessary causes we can prevent effects e g remove the hammer and the gun will not fire Preconditions don t do anything just because a gun has all its parts doesn t mean it will fire Necessary conditions are also difficult to identify since the scientific enterprise can reveal unexpectedly that what was once supposed necessary is not pin firing Partial or contributory causes Tad The problem with our schools is the teachers There are too many incompetent teachers who either don t know how to teach or just don t care about teaching any more Ruby I think parents are a big part of the problem too Lots of parents fail to read to their children never help them with homework and don t make sure their kids get to bed on time Tad So