Confirmation Falsification and Fallibility Review Valid argument An argument in which if the premises are true the conclusion must also be true Sound argument An argument which is valid and has true premises Sound arguments provide justification since they compel belief in the conclusion Review 2 Conditional statements are true except When the antecedent is true and the consequent is false If you attend class you will pass the course True True True True False False False True False False False True Note conditional statements are not arguments A only if B says the same thing as If A then B A unless B says the same thing as If not B then A or If not A then B 1 Review 3 Valid argument forms If A then B A B Modus ponens If A then B Not B Not A Modus tollens Invalid argument forms If A then B If A then B B Not A Not B A Denying the antecedent Affirming the consequent XXX XXX Review 4 When it rains in San Diego it snows in Julian It is not snowing in Julian so it is not raining in San Diego When it rains in San Diego it snows in Julian It is not snowing in Julian It is not raining in San Diego Deficits increase only if unemployment increases Unemployment is increasing Thus the deficit is increasing If deficits increase then unemployment increases Unemployment is increasing The deficit is increasing The simple model of falsifying a hypothesis The basic idea that false predictions count against the truth of a hypothesis is captured in the following argument schema If the hypothesis is true then the prediction will be true The prediction is not true The hypothesis is not true This argument form is modus tollens It is valid The question is whether the premises are true 2 A compelling simple example of falsification Where do plants get their body mass from Natural assumption from the soil In 1649 Jan Baptista van Helmont grew a willow tree for five years in a measured amount of soil adding only water The tree increased in weight by 164 pounds while the soil diminished by only two ounces If soil is the source of the mass of trees then the weight of the soil should diminish as the tree grows The weight of the soil does not diminish as the tree grows The soil is not the source of the mass of trees Galen s two bloods According to Galenic physiology arteries and veins each carried different types of blood away from the heart Venous blood carried nutrients from the liver through the right side of the heart to the body Arterial blood is vivified by the lungs and carried from the left side of the heart to the body Slight seepage from right to left Heart operated to suck blood in from the veins and ultimately from the liver Both types of blood were consumed by the body s tissues William Harvey s evidence against Galen Determined that the valves in the veins would only permit flow into the heart not out But the Galenic theory predicted that blood could flow away from the heart in the veins If the Galenic theory were right valves should permit outward flow from the heart into the veins Valves do not permit outward flow from the heart The Galenic theory is wrong 3 William Harvey s evidence against Galen 2 An assumption of the Galenic theory is that all the contents of arterial and venous blood originate in food and is dispersed Prediction the mass of food and drink must equal the mass of the material in the arterial and venous blood Harvey measured the amount of blood in the heart at a time approx 2 ounces and multiplied by number of heart beats an hour 2 000 estimated that 40 pounds of blood sent out per hour This exceeded the amount of food and liquid a person consumes and where does it all go If Galenic theory is right people need to replenish the stuff of blood from food and drink People do not eat or drink enough to replenish the stuff of blood Galenic theory is wrong Holding on to hypotheses despite falsification It is infrequent that a scientist will give up a hypothesis as soon as a prediction fails Why An accepted hypothesis often has lots of evidence it its favor things it explains Even a flawed hypothesis is better than no hypothesis Without an alternative theory stay with what has worked so far Often the prediction depends not just on the hypothesis but on other auxiliary conditions These rather than the hypothesis itself could be what is false The endurance of the caloric theory of heat The ability to heat a cold body by placing it next to a warm one suggested the hypothesis that heat is a fluid In the 18th century heat caloric was treated like other newly discovered fluids such as electricity Suggests that heat can be conserved Complexity different substances warmed differently by same source of heat 1 liter of 100 C water will warm a liter of 0 C water to 50 but 0 C mercury to approx 97 C 4 Count Rumford s aka Benjamin Thompson s experiment Friction from boring out a cannon heats the metal but there is no source from which caloric is transferred Maybe the caloric is contained in pockets within the metal But slow boring with a dull knife produced more heat than rapid boring which would unseal more pockets Rumford s reasoning If caloric a fluid is responsible for heat drilling a cannon with a bit should not produce heat Drilling a cannon with a bit did release heat lots of it Caloric is not responsible for heat Endurance of caloric theory Caloric had been named by Lavoisier after he rejected phlogiston After Lavoisier was executed Rumford married Mme Lavoisier I think I shall live to drive caloric off the stage as the late Lavoisier drove away phlogiston What a singular destiny for the wife of two Philosophers But caloric survived Rumford and Mme Lavoisier divorced him Caloric theory had a great deal of explanatory power such as the ability to explain the movement of heat through a vacuum 5 The final demise of caloric James Joule discovered in 1840 that the an electric current I flowing through a resistance R generated a rate of heating I2R Joule calculated the mechanical energy needed to produce one BTU of heat Relating heat to mechanical energy provided an alternative conception of heat With the development of an alternative theory linking heat to mechanical energy the caloric theory was finally displaced The gap between hypothesis and prediction Few interesting hypotheses lead to prediction all on their own There are typically a host of other factors at work Other hypotheses auxiliary assumptions that are assumed to be true and required to make the prediction Features of the