Logic

Logic (Greek λογίζω I reckon, I count, from λόγος a word) is that branch of philosophy that deals with and attempts to guide the faculty of human reason.

What is logic?

The Greek verb λογίζω actually occurs in the context of a marketplace transaction; the "reckoning" to which it refers is of the cash settlement of that transaction. More broadly, the verb refers to a person's understanding of the world around him, and of his actions and the consequences of those actions.

Even more broadly, one's view of logic depends on one's view of the world, and of whether things beyond man are "real," and to what extent. Four views on the subject have been current at various times in human history:

• Objectivism, or logical objectivism, states that reality is what it is, and the principles of logic are what they are, independent of any person's perception of them or efforts (or lack of effort) to understand them.
• Subjectivism, or logical subjectivism, states that what we call the "laws of nature" are merely our attempts to understand nature, and are not fundamental properties of nature.
• Logical positivism states that human beings know only that which they directly perceive and register in their minds.
• Solipsism holds that nothing is provably real except the fundamental facility of human consciousness--in other words, nothing that a human being sees need be real.

Whether anything is provably real beyond the self, and if so, what, is one of the most important decisions that a human being will ever make. To return to the cash-reckoning analogy that the original Greek word suggests: if the cash settlement is objectively provable, then both parties can agree upon it and close the transaction amicably. If, however, reality is only what one perceives, then either party may perceive the transaction in a manner to his own advantage, and need not agree with the other party. As a result, an amicable settlement might not be possible, or if it is, then it is unreliable and depends on skill at negotiation (or emotional manipulation), or even on whim.

Therefore, logic constitutes the framework for agreement between and among human beings, as to the nature of the earth and the cosmos, and as to any person's responsibilities to himself and to others.

Types of logic

Three major categories or branches of logic are acknowledged to exist:

1. Informal logic consists of "common sense" and other, rather loose rules that people employ while making most decisions and even in debate. It is unstructured, and depends largely on one's view of "the reasonable"--which in turn is that body of facts that one reasonably expects to exist. Informal logic also includes inductive reasoning. The thresholds of what is "reasonable" and what is not, are inexact and subject to change with the receipt of sufficient contrary evidence--and again, what constitutes "sufficiency" in this context might vary from person to person. Most logical fallacies are failures in informal logic.

1. Formal logic is a highly structured set of rules for deductive reasoning. Formal logic depends totally on mutual agreement between and among parties to any discussion on fundamental premises and other facts asserted as evidence. If the parties cannot agree on fact, then formal logic is unavailing. Some logical fallacies are formal-logical failures.

1. Symbolic logic is an abstract language, similar to the language of algebra, that uses variable names for propositions and various symbolic operators to stand for formal logical processes like conjunction (p and q), disjunction (p or q or both), and implication (p implies q or if p, then q). Symbolic logic differs from formal logic only in that the latter is written in the same language in which human beings regularly write and speak, whereas symbolic logic uses a language of its own.

Uses of logic in other disciplines

Logic is a necessary discipline in philosophy, because it deals with how we study and interact with the world and with other people in it. Logic is also an integral part of mathematics, dealing as it does with why certain mathematical facts follow from other, more basic facts. For example, given a standard definition of the area of a rectangle as "a measure of the interior of the rectangle, expressed as the product of the lengths of any two adjacent sides of it," one can use logic to prove area formulas for the parallelogram, the triangle, and the circle, to name three examples. All of these formulas follow, directly or indirectly, from that initial definition of the area of a rectangle.

In computer science, logic dictates how a machine will follow a set of instructions, including how to test its "world," evaluate it, and act according to that evaluation. Every computer language includes its own version of the language of symbolic logic, except that instead of establishing propositions, a computer following a program is usually choosing between and among different commands to execute.

Logic, and especially formal logic, inform the discipline of critical thinking--which, by no coincidence, takes its name from the Greek word for a judge. Indeed, judges and juries in courts of law must apply logic, both formal and informal, to arrive at their decisions. Formal logic will usually serve to state what obedience to a given body of law requires; informal logic must usually serve a trier of fact charged with deciding whether a given person was in obedience or in violation. The latter principle holds primarily because plaintiff and defendant in a court of law quite often do not agree on matters of fact.

Related Reference

• Logic by CreationWiki

See Also

• Branden, Nathaniel, The Benefits and Hazards of the Philosophy of Ayn Rand
• Rand, Ayn, The Virtue of Selfishness and other collections of essays