Understanding Deductive Reasoning in Science

Deductive reasoning goes from general to specific by starting with a given set premises and draws conclusions from them. The conclusions made from deductive reasoning are only as valid as the premises that are used such that only one false premise can produce a false conclusion. A deductive argument is considered valid if its truth necessarily follows from the starting premises and it is sound if the argument is valid and all of its premises are true other wise it is considered unsound.

A common form of deductive reasoning is called a syllogism It has three parts.

All X has y.

A general characteristic of a category of objects.

A is X.

The object under discussion belongs to that category

A has y.

The conclusion that the object under discussion has that general characteristic.

Deductive reasoning is heavily dependent on the validity of premises being used. The premises used may be facts derived from observation or a totally philosophical assumption.

A good example comes from proponents of the Big Bang Cosmology. All observations of the universe are constant with the Earth being near the center of the universe. Starting with the philosophical assumption that we are totally the result of natural process; as opposed to being created by God; it is a logically valid conclusion that we can not be in a special place in the universe such as the center. As a result they invented an explanation for the evidence that eliminate the center by making all locations seem to be at the center. However if we were created by God then we could easily be near the center of the universe. This is why Creationists and Evolutionists can look at the same evidence and draw totally different conclusions.

Deductive reasoning is a very useful tool of reasoning however it does have its difficulties. It depends heavily on the accuracy its starting premises. However flawed premises result in flawed conclusions. These difficulties need to be properly understood to properly understand scientific statements including those of both Creationists and Evolutionists.

A Discussion of Inductive Reasoning

Inductive reasoning is reasoning that draws a general conclusion based on a set of examples.

Basic pattern of Inductive Reasoning

a, b, c, d, e, f, g and h are part of group A.

a, b, c, d, e, f, g and h have property G.

All member of group A have property G.

When used in Science the process starts with observations and looks for the patterns in the observations to develop a hypothesis as general description of the observations. Inductive Reasoning allows for general conclusions to be drawn from specific observations and evidence. It there by allows conclusions based on patterns in observations and evidence. Inductive Reasoning risks the possibility that the sample size may be too small for a general conclusion. It is prone to being affected by philosophical assumptions and biases in selection of sample, in the patterns recognized, and in conclusions

Reasonable Logic

Logic is the set of principles and rules for reasoning. If it is used correctly and has the right starting point one will arrive at the correct conclusion.

Deductive reasoning is reasoning that starts with a given set premises and draws a conclusion. Inductive reasoning is reasoning that draws a general conclusion based on a set of examples. So deductive reasoning goes from general principles to specific conclusions. Inductive reasoning goes from specific principles to general conclusions. Both forms of logic are used in science.

Inductive and Deductive reasoning are different and even opposite concepts but in practice deductive and inductive reasoning are often used together even without knowing it.  For example one may be drawing a general conclusion form observed evidence (induction) based on general principles called assumptions. (deduction)

Logical fallacies are mistakes in reasoning and can be both deliberate and accidental. It is important to avoid them since they resultant in erroneous conclusions.

A Discussion of Logical Fallacies in Logic

Logical Fallacy: An error within a logical argument that is a flaw in the argument’s structure that is said to invalidate the argument.

A logical fallacy is independent of the truth so a fallacy does not necessarily invalidate the argument's premises and conclusions. However arguments derived from logical fallacies often do lead to an incorrect conclusion due to faulty reasoning.

Examples

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Ad hominem

Latin: “To the Man”
It is an argument that attacks people holding a particular point of view rather than attacking the point of view itself.
Example: The case where an opponent starts insulting you in some manner rather than countering your argument.

Overgeneralization

It is an argument which makes a statement so broad as to exceed the original point that was trying to be proved.
Often it involves taking a small sample and generalizing it to the whole group.

Non sequitur

Latin: "It does not follow"
It is an argument which moves from a premise to a conclusion where no connection exists between the two.

Proof by authority

It is an argument which is based on a person's authority, rather than on the merits of the authority's position.
Example: A argument is assumed correct because it comes from a person with a PHD.

Proof by assertion

It is an argument which simply states something as true without evidence or argument to support it.

Circular reasoning

It is an argument that tries to prove something by first asserting it and then trying to "prove" it.

Straw man

It is an argument where a person argues against a position similar to but weaker than their opponent’s real position.

Manufacturing facts from a theory

It is an undemonstrated or unobserved idea that is stated as fact because it agrees with a particular theory.

Your theory does not work under my theory, so your theory must be wrong

Often used by Evolutionists against Creationists it is a form of circular reasoning where the person tries to disprove a point of view by interpreting the facts through a different view.
Originated from discussions with evolutionists, where interpretation from Evolutionary theories are used as arguments against Creation Scienc, despite the fact that Creation Science interprets the same thing differently.

There are many more logical fallacies avoid them.