'Logically' Social (II)

(last of two parts)

Kinds of Reasoning

 © 2010 by Jensen DG. Mañebog

…WE WERE TAUGHT THAT IN COMMUNICATION, we use words, sentences, and paragraphs. Words compose a sentence and sentences in turn compose a paragraph. We would notice that many of our paragraphs contain reasoning which is in the form of arguments.

Argument basically is a group of statements, one of which is the conclusion (what is being proved) and the rest are the premises (the bases for the conclusion).

We use two kinds of argument based on the two kinds of reasoning that we make: deductive and inductive. A reasoning or argument is deductive if the premises claim to give conclusive grounds for the truth of the conclusion, or if the premises claim to support the conclusion with necessity. Deductive argument is therefore either valid or invalid. In a valid deductive argument, the conclusion follows necessarily from the premises. Consider this argument:

This argument is valid. Once we we assume the premises All dogs are mammals and Canines are dogs as both true, we are necessitated to accept the conclusion Canines are mammals as also true. It will be inconsistent and self-contradictory to accept these premises but deny its conclusion, because the conclusion necessarily follows from the premises.

In contrast, in an invalid deductive argument, the conclusion does not follow necessarily from the premise/s. Consider this argument:

Senna loves good food; therefore, she will be an excellent chef.

This argument is invalid because the conclusion does not follow necessarily from the premise. Even if we accept the premise Senna loves good food as true, the conclusion She will be an excellent chef remains to be either true or false. Meaning, there will be no inconsistency to regard the conclusion as false while accepting the premise as true. Senna’s love of good food does not guarantee that she will be able to cook well.

When you reason inductively on the other hand, you infer a general conclusion from a collection of particular facts. For example, you might conclude that “All flowers are fragrant” because “Ilang-ilang”, “Sampaguita”, “Rose”, “Rosal” and “Wild Orchid” are fragrant.

Whereas deductive argument is either valid or invalid, inductive argument is either reliable or unreliable. For inductive reasoning to be reliable, the conclusion must be based on ample amount of individual representative instances. Consider, for example, the following argument:

According to a certain survey, 385 of the 500 respondents say they would like Mr. Crisostomo to be the next mayor in our town. Therefore, the majority of our voters would vote for him if he decides to run for the position.

In this argument, whether or not the evidence is adequate depends. In a town of 5,000, the 500 citizens are a ten percent sample, perhaps enough for the purposes of survey for election. But in a town of 60,000 residents, the respondents would amount to less than one percent of the total number of residents, an insufficient sample on which to base a conclusion regarding the possible election result.

Whether or not the evidence is representative again depends. We may believe that the survey presents representative sample if we knew that it was thoroughly constructed to reflect the sex, age, race, civil status, job, religion, and income of the town’s populace as a whole.

Do not confuse inductive argument with invalid deductive argument. The difference between deduction and induction is not the difference between good and bad reasoning, but between two ways to support the truth of conclusions.

In creating argumentative paragraph in writing or speaking, Logic prescribes that we can use both valid deductive and reliable inductive argument …

Example:

Charles Darwin

….Darwin himself eventually grew away from his traditional faith. He concluded that “the whole subject is beyond the scope of man’s intellect…The mystery of the beginning of all things is insoluble for us; and I for one must be content to remain an Agnostic.”

Nonetheless, he was buried with full national honors beside Isaac Newton at Westminster Abbey, and eulogies on him were preached there and at St. Paul’s Cathedral, London. By the time of his death, many Christians had already come to terms with the theory of evolution, finding it not incompatible with Christian faith. Even the highly conservative papacy did not place any of Darwin’s books on the Index of Forbidden Books, nor was evolution mentioned in Pius IX’s Syllabus of Errors (1864). The first reservations were expressed in The Catholic Encyclopedia (1909), but on scientific, not theological, grounds…..

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