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The corresponding conditional of a valid argument is a logical truth and the negation of its corresponding conditional is a contradiction. The conclusion is a necessary consequence of its premises. An argument that is not valid is said to be "invalid". An example of a valid (and sound) argument is given by the following well-known syllogism:
As the study of argument is of clear importance to the reasons that we hold things to be true, logic is of essential importance to rationality. Arguments may be logical if they are "conducted or assessed according to strict principles of validity", [1] while they are rational according to the broader requirement that they are based on reason and knowledge.
Reason is the capacity of consciously applying logic by drawing valid conclusions from new or existing information, with the aim of seeking the truth. [1] It is associated with such characteristically human activities as philosophy, religion, science, language, mathematics, and art, and is normally considered to be a distinguishing ability possessed by humans.
Other ways to express this are that there is no reason to accept the premises unless one already believes the conclusion, or that the premises provide no independent ground or evidence for the conclusion. [3] Circular reasoning is closely related to begging the question, and in modern usage the two generally refer to the same thing. [4]
Deductively valid inferences are the most reliable form of inference: it is impossible for their conclusion to be false if all the premises are true. [34] [35] This means that the truth of the premises ensures the truth of the conclusion. A deductive argument is sound if it is valid and all its premises are true. [36]
Being a valid argument does not necessarily mean the conclusion will be true. It is valid because if the premises are true, then the conclusion has to be true. This can be proven for any valid argument form using a truth table which shows that there is no situation in which there are all true premises and a false conclusion. [2]
1. an assured statement made; 2. completion of a will and all its parts to make it valid and legal; 3). book of facts and law presented in a Canadian court. favor contractus: favor of the contract A concept in treaty law that prefers the maintaining of a contract over letting it expire for purely procedural reasons. felo de se: felon of himself ...
The phrase is distinct from reductio ad absurdum, which is usually a valid logical argument. ab abusu ad usum non valet consequentia: The inference of a use from its abuse is not valid: i.e., a right is still a right even if it is abused (e.g. practiced in a morally/ethically wrong way); cf. § abusus non tollit usum. ab aeterno: from the eternal