The law of non-contradiction is a fundamental principle in classical logic, stating that contradictory propositions cannot both be true in the same sense at the same time. For example, the two propositions the house is white and the house is not white are mutually exclusive. The law is expressed as the tautology ¬(p ∧ ¬p), or in words: the house is not both white and not white.
The law of non-contradiction is considered to be universally true by most philosophers, including Aristotle, who asserted that the most certain of all basic logic principles is that contradictory propositions are not true simultaneously. However, some modern logical systems, such as paraconsistent logic, reject the principle of explosion, which states that anything follows from a contradiction.
The law of non-contradiction is closely tied to the notion of rationality and is considered foundational to human thinking and speaking. It is also considered necessary for theology and all other intellectual disciplines.
The law of non-contradiction has been used to argue against the existence of God, particularly in the case of the Christian God, who is described as having qualities that are mutually exclusive, such as being omnipotent but unable to lie. However, theologians and philosophers have also argued that God is beyond human logic and that apparent contradictions in religious texts are a result of humans' limited understanding of God.
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The law of non-contradiction and the law of excluded middle
The law of non-contradiction states that contradictory propositions cannot both be true in the same sense at the same time. For example, the two propositions "the house is white" and "the house is not white" are mutually exclusive. Formally, this is expressed as the tautology ¬(p ∧ ¬p).
The law of non-contradiction is one of the three laws of thought, along with the law of excluded middle and the law of identity. The law of excluded middle states that at least one of two propositions like "the house is white" and "the house is not white" holds. The law of identity states that A is A.
The law of non-contradiction is considered to be necessarily true universally (in all possible worlds) by most philosophers, including Aristotle, who asserted that the most certain of all basic logic principles is that contradictory propositions are not true simultaneously. However, this is not immune to attacks from skeptics from modern logical pluralism, which holds the view that there is more than one correct logic.
Different logics disagree about which argument forms are valid. For example, Classical and Strong Kleene logic tell us that the principle of explosion, or ex falso quodlibet, is valid, whereas Relevant logics and other Paraconsistent logics say that this argument form is not valid. It’s natural to think that they can’t all be right. If ex falso quodlibet is valid, then Relevant and Paraconsistent logics are not correct theories of validity. Alternatively, if ex falso quodlibet is not valid, then Classical logic and Strong Kleene logic are not correct. Logical pluralism, in its most philosophically interesting and controversial forms, holds that more than one logic can be correct.
Another similar basic law of thought, the law of excluded middle, is heavily challenged within mathematics by the modern constructivism school led by Brouwer against Hilbert's formalism. Intuitionistic logic, sometimes more generally called constructive logic, refers to systems of symbolic logic that differ from the systems used for classical logic by more closely mirroring the notion of constructive proof. Formalized intuitionistic logic was originally developed by Arend Heyting to provide a formal basis for Brouwer's programme of intuitionism. From a proof-theoretic perspective, Heyting’s calculus is a restriction of classical logic in which the law of excluded middle and double negation elimination have been removed.
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The law of non-contradiction and the principle of explosion
The law of non-contradiction (LNC) is a fundamental principle in classical logic, stating that contradictory propositions cannot both be true in the same sense at the same time. For example, the two propositions "the house is white" and "the house is not white" are mutually exclusive. Formally, this is expressed as ¬(p ∧ ¬p).
The LNC is closely tied to the notion of rationality and is considered a necessary foundation for rationality and theology. The LNC is also one of the three laws of thought, along with the law of excluded middle and the law of identity.
However, the LNC has been challenged and debated, particularly in the fields of theology and philosophy. Some argue that the LNC is not universally valid and that there are situations where it does not apply or is false. For example, John V. Dahms proposed that the LNC has limited applicability and that there are areas of life, such as ethics and aesthetics, where logic and the LNC do not apply. He also cited Christian doctrines, such as the Trinity and the Incarnation, as examples of religious truths that challenge the universal applicability of the LNC.
In response, Norman Geisler defended the universality of the LNC, arguing that all forms of thought and logic must use the LNC. He refuted Dahms' examples, stating that they were either not true contradictions or were self-defeating arguments. Geisler also emphasized that the LNC is necessary for meaningful communication and understanding, as without it, statements and thoughts about reality become meaningless and incoherent.
Another concept related to the LNC is the principle of explosion, which states that anything follows from a contradiction. This principle is used in reductio ad absurdum proofs.
While the LNC is widely accepted as a fundamental principle of logic, there are differing views and ongoing debates about its universality and applicability in certain fields, such as theology and philosophy.
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The law of non-contradiction and the law of identity
The law of non-contradiction is foundational to human thinking and speaking and is closely tied to the notion of rationality. It is a necessary foundation for theology and other intellectual disciplines. It is also a necessary component of human rationality as imagers of God and is necessary for knowing anything.
The law of non-contradiction is necessary for making faith and life intelligible. Without it, the concept of truth loses all meaning. For example, if God told Adam and Eve not to eat the fruit, and if contradiction and truth were compatible, God could not have condemned Adam and Eve for eating the fruit. God's prohibition against eating the fruit could have meant both "do not eat the fruit" and "you may eat the fruit" at the same time and in the same sense.
The law of non-contradiction is also necessary for distinguishing categories. If this law is violated, a collection of letters, w-a-t-e-r, could mean not only sulfuric acid but also, at the same time and in the same sentence, tree, stone, Arcturus, the preposition because, and so on. If a word can mean everything, it means nothing.
The law of non-contradiction is also necessary for communication. If this law is violated, it becomes impossible to know what to believe or in whom to put our trust.
The law of non-contradiction is also necessary for meaningful revelation. If the Bible contains contradictions, it reveals nothing meaningful at those points.
The law of non-contradiction is also necessary for making faith meaningful. If faith involves what one believes and knows, and if rationality is necessary for the faith, then the law of non-contradiction is necessary for faith.
The law of non-contradiction is also necessary for making statements about reality. If this law is violated, it becomes impossible to make logical statements or deductions about reality.
The law of non-contradiction is also necessary for making statements about God. If this law is violated, it becomes impossible to distinguish any categories about God.
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The law of non-contradiction and logical pluralism
The law of non-contradiction (LNC) is a fundamental principle in classical logic, stating that contradictory propositions cannot both be true in the same sense at the same time. For example, the two propositions "the house is white" and "the house is not white" cannot both be true.
The LNC is considered to be necessarily true and universally applicable by most philosophers, including Aristotle, who asserted that it is the most certain of all basic logic principles. However, the LNC has been challenged by modern logical pluralism, which holds that there is more than one correct logic. Different logics disagree about which argument forms are valid, and logical pluralism asserts that multiple logics can be correct simultaneously. For example, while Classical and Strong Kleene logic consider the principle of explosion (i.e., that anything follows from a contradiction) to be valid, Relevant logics and other Paraconsistent logics reject it.
The LNC is closely tied to the notion of rationality and is necessary for understanding, describing, and communicating about reality. Violating the LNC leads to a breakdown in meaningful communication, as words and sentences lose their ability to convey specific meanings. However, some have argued that the LNC has limited applicability or that it can be violated in certain areas, such as ethics, mathematics, and religious knowledge.
In the context of religious epistemology, some have challenged the universality of the LNC, particularly when applied to certain doctrines of the faith. For example, John V. Dahms argues that the LNC does not apply to the Biblical view of the cross, the two natures of Christ, or the Trinity. He claims that logic has limited applicability and that other criteria, such as aesthetic judgment, can be used in areas where logic leaves off. However, critics of this view argue that without the LNC, meaningful communication about religious doctrines becomes impossible, as any meaning can be assigned to theological concepts.
Overall, while the LNC is widely accepted as a fundamental principle of logic, challenges to its universality and attempts to violate it have arisen, particularly in the realm of religious knowledge and logical pluralism.
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The law of non-contradiction and the law of excluded middle
The law of non-contradiction (LNC) and the law of excluded middle (LEM) are two of the three laws of thought, the third being the law of identity. The LNC states that contradictory propositions cannot both be true in the same sense at the same time. The LEM states that at least one of two propositions must be true, e.g. "the house is white" or "the house is not white".
The LNC and the LEM are closely related. Together, they create a dichotomy in a logical space, with each combination containing exactly one member of each pair of contradictory propositions. The LNC expresses the mutually exclusive aspect of this dichotomy, and the LEM expresses its jointly exhaustive aspect.
The LNC is foundational to human thinking and speaking. It is necessary for distinguishing categories, conveying meanings, exposing irrationalities, and differentiating truth from falsehood. The LNC is also a prerequisite for rationality, as rationality involves the proper use of reason to understand and describe reality.
However, the LNC has been challenged, particularly in the context of religious knowledge and theology. Some argue that the LNC does not apply to certain doctrines of the faith, such as the Trinity, the Incarnation, and divine sovereignty and free will. They claim that these doctrines are paradoxical or mysterious, and that our finite human understanding cannot fully grasp their true meaning.
Others defend the universality of the LNC, arguing that without it, meaningful communication and understanding become impossible. They assert that the LNC is necessary for making faith and religious knowledge intelligible and that any apparent contradictions in religious texts should be resolved or interpreted in a way that does not violate the LNC.
While the LNC is widely accepted as a fundamental principle of logic, its application to specific areas, such as theology, remains a subject of debate.
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Frequently asked questions
The law of non-contradiction states that contradictory propositions cannot both be true in the same sense at the same time. Formally, this is expressed as the tautology ¬(p ∧ ¬p). For example, it is tautologous to say "the house is not both white and not white" since this results from putting "the house is white" in that formula, yielding "not (the house is white and not (the house is white))", then rewriting this in natural English.
The law of non-contradiction is a foundational law in classical logic and is considered to be necessarily true universally. It is closely tied to the notion of rationality and is a necessary foundation for it. God's judgment on disobedience demonstrates that the Bible assumes the existence of one of the fundamental laws of reason, the law of non-contradiction. This law is vital to the intelligibility of faith and life. Without it, the concept of truth loses all meaning.
The law of non-contradiction is used to argue against the idea of God being omnipotent. For instance, could an omnipotent being create an indestructible object, and then destroy it? This is an inherent contradiction.