Deductive reasoning

Students of media department can use deductive reasoning to better understand the world around them. 

Deductive reasoning is a logical process in which a conclusion is based on the concordance of multiple premises that are generally assumed to be true. Deductive reasoning is sometimes referred to as top-down logic. Its counterpart, inductive reasoning, is sometimes referred to as bottom-up logic.

Deductive reasoning is a logical process in which a conclusion drawn from a set of premises contains no more information than the premises taken collectively. All dogs are animals; this is a dog; therefore, this is an animal: The truth of the conclusion is dependent only on the method.

Premise

LOGIC

A previous statement or proposition from which another is inferred or follows as a conclusion.

"If the premise is true, then the conclusion must be true"

an assertion or proposition which forms the basis for a work or theory.

"the fundamental premise of the report"

synonyms:

proposition, assumption, hypothesis, thesis, presupposition, postulation, postulate, supposition, presumption, surmise, conjecture, speculation, datum, argument, assertion, belief, thought;  premiss "a philosophy based on the premise that human life consists of a series of choices" verb

base an argument, theory, or undertaking on.

"the reforms were premised on our findings"

·         state or presuppose (something) as a premise.

"one school of thought premised that the cosmos is indestructible"

synonyms:

postulate, hypothesize, conjecture, posit, theorize, suppose, presuppose, surmise, assume, predicate, argue, state, assert;  rare hypothecate "one school of thought premised that the cosmos is indestructible"

Concordance

an alphabetical list of the words (especially the important ones) present in a text or texts, usually with citations of the passages concerned or with the context displayed on a computer screen.

"a concordance to the Bible"

1.    2.

formal

agreement or consistency.

"the concordance between the teams' research results"

Deductive reasoning

Deductive reasoning is a basic form of valid reasoning. Deductive reasoning, or deduction, starts out with a general statement, or hypothesis, and examines the possibilities to reach a specific, logical conclusion, according to the University of California. The scientific method uses deduction to test hypotheses and theories. The scientific method uses deduction to test hypotheses and theories. "In deductive inference, we hold a theory and based on it we make a prediction of its consequences. That is, we predict what the observations should be if the theory were correct.  We go from the general — the theory — to the specific — the observations," said Dr. Sylvia Wassertheil-Smoller, a researcher and professor emerita at Albert Einstein College of Medicine.

In deductive reasoning, if something is true of a class of things in general, it is also true for all members of that class. For example, "All men are mortal. Harold is a man. Therefore, Harold is mortal." For deductive reasoning to be sound, the hypothesis must be correct. It is assumed that the premises, "All men are mortal" and "Harold is a man" are true. Therefore, the conclusion is logical and true.

According to the University of California, deductive inference conclusions are certain provided the premises are true. It's possible to come to a logical conclusion even if the generalization is not true. If the generalization is wrong, the conclusion may be logical, but it may also be untrue. For example, the argument, "All bald men are grandfathers. Harold is bald. Therefore, Harold is a grandfather," is valid logically but it is untrue because the original statement is false.

A common form of deductive reasoning is the syllogism, in which two statements — a major premise and a minor premise — reach a logical conclusion. For example, the premise "Every A is B" could be followed by another premise, "This C is A." Those statements would lead to the conclusion "This C is B." Syllogisms are considered a good way to test deductive reasoning to make sure the argument is valid.

In an inductive argument, the premises are intended only to be so strong that, if they were true, then it would be unlikely that the conclusion is false. There is no standard term for a successful inductive argument. But its success or strength is a matter of degree, unlike with deductive arguments.

Therefore, inductive reasoning moves from specific instances into a generalized conclusion, while deductive reasoning moves from generalized principles that are known to be true to a true and specific conclusion. The accuracy of inductive reasoning is questionable.

During the scientific process, deductive reasoning is used to reach a logical true conclusion. Another type of reasoning, inductive, is also used. Often, deductive reasoning and inductive reasoning are confused. It is important to learn the meaning of each type of reasoning so that proper logic can be identified.

Deductive Reasoning Examples

Deductive reasoning is a type of reasoning which goes from general to specific. Deductive reasoning is based on premises and if the premises are true, then the reasoning will be valid.

Deductive Reasoning: Everyday Examples

·         In mathematics, If A = B and B = C, then A = C.

·         Since all humans are mortal, and I am a human, then I am mortal. 

·         All dolphins are mammals, all mammals have kidneys; therefore all dolphins have kidneys. 

·         Since all squares are rectangles, and all rectangles have four sides, so all squares have four sides. 

·         If Dennis misses work and at work there is a party, then Dennis will miss the party.

·         All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a 5, so it is divisible by 5.

·         To earn a master’s degree, a student must have 32 credits. Tim has 40 credits, so Tim will earn a master’s degree.

·         All birds have feathers and robins are birds, so robins have feathers.

·         It is dangerous to drive on icy streets. The streets are icy now so it is dangerous to drive now.

·         All cats have a keen sense of smell. Fluffy is a cat, so Fluffy has a keen sense of smell.

·         Snakes are reptiles and reptiles are cold-blooded; therefore, snakes are cold-blooded.

·         Cacti are plants and all plants perform photosynthesis; therefore, cacti perform photosynthesis.

·         Red meat has iron in it and beef is red meat, so beef has iron in it.

·         Acute angles are less than 90 degrees and this angle is 40 degrees so this angle is acute.

·         All noble gases are stable and helium is a noble gas, so helium is stable.

·         Magnolias are dicots and dicots have two embryonic leaves; therefore magnolias have two embryonic leaves.

·         Elephants have cells in their bodies and all cells have DNA, so elephants have DNA.

·         All cars have at least two doors and a Ford Focus is a car, so the Ford Focus has at least two doors.

·         All horses have manes and the Arabian is a horse; therefore Arabians have manes.

Other Patterns of Deductive Reasoning 

Some deductive reasoning does not follow the classic reasoning pattern of A = B and B = C, then A = C. Some examples of other patterns are:

·         Be careful around bees, they might sting you. (The reasoning is understood that all bees might sting.)

·         It takes me an hour to get to the mall. If I leave at five o’clock I will reach the mall by six o’clock.

·         That dog is growling so be careful or you might get bitten. (It is logical is the dog is angry, he might bite.)

·         The apple hit me on the head because of gravity. 

·         There are three people in my family. Each one is tall, so everyone in my family is tall.