Inference in Arguments

In logic, an inference is a process of deriving logical conclusions from premises known or assumed to be true. The term derives from the Latin term, which means "bring in."

An inference is said to be valid if it's based upon sound evidence and the conclusion follows logically from the premises.

Examples and Observations

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What Is Deductive Reasoning?

By Richard Nordquist

Arthur Conan Doyle: From a drop of water, a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other.

Sharon Begley: [James] Watson, of course, shared the 1962 Nobel Prize in Medicine or Physiology for discovering, with the late Francis Crick, the double-helix structure of DNA, the master molecule of heredity. In his chronicle of that achievement, The Double Helix, Watson cast himself as the swashbuckling genius fighting his way to the top, climbing over anyone who got in his way (including Rosalind Franklin, who took the x-ray images that formed the basis for Watson and Crick's inference about DNA's structure but whom Watson and Crick failed to credit at the time).

Steven Pinker: [T]he mind has to get something out of forming categories, and that something is inference. Obviously, we can't know everything about every object. But we can observe some of its properties, assign it to a category, and from the category predict properties that we have not observed. If Mopsy has long ears, he is a rabbit; if he is a rabbit, he should eat carrots, go hippety-hop, and breed like, well, a rabbit. The smaller the category, the better the prediction. Knowing that Peter is a cottontail, we can predict that he grows, breathes, moves, was ​suckled, inhabits open country or woodland clearings, spreads tularemia, and can contract myxomatosis. If we knew only that he was a mammal, the list would include only growing, breathing, moving, and being suckled. If we knew only that he was an animal, it would shrink to growing, breathing, and moving.

S.I. Hayakawa: An inference, as we shall use the term, is a statement about the unknown made on the basis of the known. We may infer from the material and cut of a woman's clothes her wealth or social position; we may infer from the character of the ruins the origin of the fire that destroyed the building; we may infer from a man's calloused hands the nature of his occupation; we may infer from a senator's vote on an armaments bill his attitude toward Russia; we may infer from the structure of land the path of a prehistoric glacier; we may infer from a halo on an unexposed photographic plate that it has been in the vicinity of radioactive materials; we may infer from the sound of an engine the condition of its connecting rods. Inferences may be carefully or carelessly made. They may be made on the basis of a broad background of previous experience with the subject matter or with no experience at all. For example, the inferences a good mechanic can make about the internal condition of a motor by listening to it are often startlingly accurate, while the inferences made by an amateur (if he tries to make any) may be entirely wrong. But the common characteristic of inferences is that they are statements about matters which are not directly known, statements made on the basis of what has been observed.

John H. Holland, Keith J. Holyoak, Richard E. Nisbett, and Paul R. Thagard: Deduction is typically distinguished from induction by the fact that only for the former is the truth of an inference guaranteed by the truth of the premises on which it is based (given that all men are mortal and that Socrates is a man, we can deduce with complete certainty that Socrates is mortal). The fact that an inference is a valid deduction, however, is no guarantee that it is of the slightest interest. For example, if we know that snow is white, we are free to apply a standard rule of deductive inference to conclude that either 'snow is white or lions wear argyle socks.' In most realistic contexts such deductions will be as worthless as they are valid.

George Eliot: A dull mind, once arriving at an inference that flatters a desire, is rarely able to retain the impression that the notion from which the inference started was purely problematic. And Dunstan's mind was as dull as the mind of a possible felon usually is.