My notes in preparation for a discussion I was hosting, which I knew would require remembrance of these definitions by some participants to keep us all on the same page. I fused multiple definitions to cover most interpretations: reason, intuition, logic, deduction, induction, fallacy, critical thinking, opinion,  argumentation, evidence, and skepticism.

Definitions for good discussions: Reason, Intuition, Logic, Deduction, Induction, Fallacy, Critical Thinking, Opinion, Facts, Argumentation, Evidence, Skepticism.


Reason is a consideration that explains or justifies events, phenomena, or behavior. It is the capacity of consciously making sense of things, establishing and verifying facts, justifying or adapting practices and beliefs based on existing or new information.

Reasoning is understanding and forming judgments, the way rational individuals understand sensory information from their environments and conceptualize abstractions. Reasoning may be subdivided into forms of logical and intuitive.

Intuition, the ability to acquire knowledge without conscious reasoning, is often necessary for the creative processes involved with arriving at a formal proof.


Logic studies ways in which humans reason formally through argument.

Deduction is a form of reasoning in which a conclusion follows necessarily from the stated premises. Deductive reasoning - deductive or "top-down" logic - is the process of reasoning from one or more statements (premises) to reach a logically certain conclusion, by applying general rules which hold over the entirety of a closed domain of discourse, narrowing the range until only the conclusion is left. If all premises are true, the terms are clear, and the rules are followed, then the conclusion reached is necessarily true.

Induction is a form of inference (arriving at a conclusion with some degree of probability), based on previous observations or experiences, or formulating general statements based on limited observations of patterns. In inductive reasoning - "bottom-up" logic - the premises supply some evidence for the probable truth of the conclusion, and the truth of the premises does not guarantee the truth of the conclusion. This conclusion of an inductive argument contains more information than is already contained in the premises.

Analogical reasoning, from a particular to a particular, is a weaker form of inductive reasoning from a single example.

Abductive reasoning, or argument to the best explanation (favoring one conclusion above others), starts with incomplete set of observations and proceeds with likely possible explanations. The conclusion does not follow with certainty from its premises and concerns something unobserved.


Flawed reasoning in arguments is known as fallacious reasoning that commits formal or informal fallacies.

  • A formal fallacy occur when there is a problem with the form of the argument. Such argument is always invalid.
  • In informal fallacy, the error in reasoning is due to a problem with the content of the argument.

Critical Thinking

Critical thinking employs not only logic but also clarity, credibility, accuracy, precision, relevance, depth, breadth, significance, and fairness.

Critical thinking skills include observation, interpretation, analysis, inference, evaluation, explanation, and meta-cognition, and the the ability to:

  1. Identify evidence through reality.
  2. Isolate the problem from context.
  3. Establish relevant criteria for judgment.
  4. Prioritize and order precedence for problem-solving.
  5. Gather relevant information.
  6. Recognize unstated assumptions and values.
  7. Comprehend and use language with accuracy.
  8. Interpret data to appraise evidence and evaluate arguments.
  9. Recognize the existence or non-existence of logical relationships.
  10. Draw and test warranted conclusions and generalizations.
  11. Reconstruct patterns of beliefs on the basis of wider experience.
  12. Render accurate judgments about specific things and qualities.


Opinions may deal with subjective matters, in which there is no conclusive finding, or with facts.

Facts are verifiable, and can be agreed to by the consensus of experts. Facts are known to be consistent with objective reality and can be proven to be true with evidence. They serve as concrete descriptions of a state of affairs on which beliefs can later be assigned.

If opinions are supported by facts and principles, they become arguments.


Argument is a series of statements (premises), intended to determine the degree of truth of another statement (conclusion).
Logic is the study of the forms of reasoning in arguments.

Deductive arguments:

  • In a valid deductive argument, premises necessitate the conclusion, even if some premises are false, and the conclusion is false.
  • In a sound argument, true premises necessitate a true conclusion.

Inductive arguments can have different degrees of logical strength: the stronger the argument, the greater the probability that the conclusion is true.

People may draw opposing conclusions (opinions) even if they agree on the same set of facts. Opinions can be persuasive, but only the assertions they are based on can be said to be true or false.

Analysis of social phenomena based on opinions is referred to as normative analysis (what ought to be), and positive analysis is based on scientific observation.

Significance, worthiness of attention, evaluative importance, seriousness, or magnitude of something  is usually an opinion.

Meaning is something conveyed by language, concept, or action - intended or not.


Evidence is anything presented in support of an assertion, which hopefully provides proof of the truth of the statement.
Scientific evidence consists of observations and experimental results that serve to support, refute, or modify a scientific hypothesis or theory, when collected and interpreted in accordance with the scientific method.

Legal evidence include testimony, documentary evidence, and physical evidence.

Epistemology is the study of the knowledge, justification, and the rationality of belief. It considers the nature of knowledge and how it can be acquired, the sources and scope of knowledge and justified belief, and the criteria for knowledge and justification.

Skepticism is a questioning attitude towards items of knowledge or dogma, and is often directed at supernatural, morality, theism, or certainty. Scientific skepticism tests beliefs for reliability and subjects them to systematic investigation using the scientific method, to discover empirical evidence for them.


Definitions for good discussions: Reason, Intuition, Logic, Deduction, Induction, Fallacy, Critical Thinking, Opinion, Facts, Argumentation, Evidence, Skepticism.

Definitions for good discussions: Reason, Intuition, Logic, Deduction, Induction, Fallacy, Critical Thinking, Opinion, Facts, Argumentation, Evidence, Skepticism.
Definitions, Reason, Intuition, Logic, Deduction, Induction, Fallacy, Critical Thinking, Opinion, Facts, Argumentation, Evidence, Skepticism.

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