A philosophical inquiry into the foundations of logic and the theory of knowledge
What the Work Is
Logic is a philosophical treatise by Edmund Husserl, the Austrian-German philosopher who established the school of phenomenology. First published in 2001, the work addresses fundamental questions in the theory of knowledge, logic, and phenomenology. The book engages with the nature of logical inquiry and the proper delimitation of logic as a field of study, concerns that reflect Husserl’s broader philosophical project of establishing a rigorous foundation for the sciences.
What the Book Is About
The central concern of Logic is the proper demarcation of logic as a scientific discipline. Husserl examines how fields of inquiry can become confused when heterogeneous subject matters are improperly combined under a single putative field-unity. He argues that such confusion arises from a fundamental misreading of the objects that a proposed science ought to investigate. The book thus addresses the question of what logic truly is, what its proper objects of study are, and how it should be distinguished from other domains of inquiry.
Key Ideas and Themes
A central theme of the work is the danger of field-delimitation errors in the sciences. Husserl identifies a particularly serious fault: the confusion of fields, where distinct domains of investigation are erroneously merged. This occurs when researchers misunderstand the essential nature of the objects their science is meant to study, leading them to combine heterogeneous elements into a false unity.
This concern reflects Husserl’s broader philosophical commitments. His early work developed critiques of psychologism in logic—the view that logical laws are merely psychological regularities of human thinking. By insisting on the proper delimitation of logic as a field, Husserl works to establish that logical truths are not reducible to empirical facts about how people happen to think. The book’s emphasis on correctly identifying the objects of logical investigation connects to this project of securing logic’s autonomy as a discipline.
The work also engages with phenomenological concerns, examining how knowledge and logical validity relate to the structures of consciousness. Husserl’s phenomenological method sought to describe the essential structures of experience and thought, and Logic applies this approach to questions about the foundations of logical and scientific knowledge.
Structure and Approach
The book opens with a discussion of the dangers inherent in improperly delimiting scientific fields. Husserl’s approach is analytical and critical, examining how errors in field-delimitation lead to fundamental misunderstandings of the objects under investigation. His method involves careful attention to the nature of the objects that a science aims to study, arguing that proper scientific practice requires a correct grasp of what those objects essentially are.
Significance and Influence
The work stands within Husserl’s larger philosophical project, which profoundly influenced twentieth-century philosophy. Husserl’s phenomenology, with its emphasis on the rigorous analysis of consciousness and its contents, shaped subsequent developments in both continental and analytic philosophy. His arguments against psychologism in logic had lasting impact on the philosophy of logic and mathematics, helping to establish the view that logical laws are normative and necessary rather than empirical and contingent.
The book’s treatment of field-delimitation and the proper objects of logical inquiry contributes to ongoing philosophical discussions about the nature of logic, the foundations of knowledge, and the relationships between different scientific disciplines. Its publication in 2001 made available to contemporary readers an important part of Husserl’s thinking on these foundational questions.
The broader historical development of logic provides essential background for understanding the stakes of Husserl’s inquiry. The history of logic deals with the study of the development of the science of valid inference. Formal logics developed in ancient times in India, China, and Greece. Greek methods, particularly Aristotelian logic as found in the Organon, found wide application and acceptance in Western science and mathematics for millennia. The Stoics, especially Chrysippus, began the development of predicate logic.
The period between the fourteenth century and the beginning of the nineteenth century saw largely decline and neglect in the study of logic. Empirical methods ruled the day, as evidenced by Sir Francis Bacon’s Novum Organon of 1620. Logic revived in the mid-nineteenth century, at the beginning of a revolutionary period when the subject developed into a rigorous and formal discipline which took as its exemplar the exact method of proof used in mathematics. The development of the modern “symbolic” or “mathematical” logic during this period by the likes of Boole, Frege, Russell, and Peano is the most significant in the two-thousand-year history of logic.
Logic in India
Logic began independently in ancient India and continued to develop to early modern times without any known influence from Greek logic. The Nasadiya Sukta of the Rigveda contains ontological speculation in terms of various logical divisions that were later recast formally as the four circles of catuskoti: “A”, “not A”, “A and ‘not A'”, and “not A and not not A”.
Public debates were common in preclassical India, as they are frequently alluded to in various Upaniṣads and in the early Buddhist literature. Assemblies comprising relevant experts were regularly convened to deliberate on administrative, legal, and religious matters. A philosopher named Dattatreya is stated in the Bhagavata Purana to have taught Anviksiki to Aiarka, Prahlada and others. The credit of founding the Anviksiki in its special sense of a science is attributed to Medhatithi Gautama (c. 6th century BC). The Mahabharata, around the 5th century BC, refers to the anviksiki and tarka schools of logic.
Pāṇini (c. 5th century BC) developed a form of logic for his formulation of Sanskrit grammar. Logic is described by Chanakya in his Arthashastra as an independent field of inquiry. Two of the six Indian schools of thought deal with logic: Nyaya and Vaisheshika. The Nyāya Sūtras of Aksapada Gautama (c. 2nd century AD) constitute the core texts of the Nyaya school. This realist school developed a rigid five-member schema of inference involving an initial premise, a reason, an example, an application, and a conclusion.
Jains made their own unique contribution to the mainstream development of logic by occupying itself with basic epistemological issues concerning the nature of knowledge, how knowledge is derived, and in what way knowledge can be said to be reliable. The Jains have doctrines of relativity used for logic and reasoning: Anekāntavāda (the theory of relative pluralism or manifoldness), Syādvāda (the theory of conditioned predication), and Nayavāda (the theory of partial standpoints).
Nagarjuna (c. 150–250 AD), the founder of the Madhyamaka (“Middle Way”), developed an analysis known as the catuṣkoṭi, a “four-cornered” system of argumentation that involves the systematic examination and rejection of each of the four possibilities of a proposition. Dignāga (c. 480–540 AD) is sometimes said to have developed a formal syllogism, and it was through him and his successor, Dharmakirti, that Buddhist logic reached its height. Their analysis centered on the definition of an inference-warranting relation, “vyapti”, also known as invariable concomitance or pervasion. Dignāga’s famous “wheel of reason” (Hetucakra) is a method of indicating when one thing can be taken as an invariable sign of another thing, but the inference is often inductive and based on past observation.
Logic in China
In China, a contemporary of Confucius, Mozi, “Master Mo”, is credited with founding the Mohist school, whose canons dealt with issues relating to valid inference and the conditions of correct conclusions. One of the schools that grew out of Mohism, the Logicians, are credited by some scholars for their early investigation of formal logic. Due to the harsh rule of Legalism in the subsequent Qin dynasty, this line of investigation disappeared in China until the introduction of Indian philosophy by Buddhists.
Logic in the Ancient Mediterranean
Valid reasoning has been employed in all periods of human history. It is probable that the idea of demonstrating a conclusion first arose in connection with geometry. The ancient Egyptians discovered geometry, including the formula for the volume of a truncated pyramid. Esagil-kin-apli’s medical Diagnostic Handbook in the 11th century BC was based on a logical set of axioms and assumptions, while Babylonian astronomers in the 8th and 7th centuries BC employed an internal logic within their predictive planetary systems.
While the ancient Egyptians empirically discovered some truths of geometry, the great achievement of the ancient Greeks was to replace empirical methods by demonstrative proof. Both Thales and Pythagoras of the Pre-Socratic philosophers seemed aware of geometric methods. Fragments of early proofs are preserved in the works of Plato and Aristotle, and the idea of a deductive system was probably known in the Pythagorean school and the Platonic Academy. The proofs of Euclid of Alexandria are a paradigm of Greek geometry.
Thales is the first known individual to use deductive reasoning applied to geometry, by deriving four corollaries to his theorem. The systematic study of proof seems to have begun with the school of Pythagoras in the late sixth century BC. The Pythagoreans, believing all was number, are the first philosophers to emphasize form rather than matter.
The writing of Heraclitus (c. 535 – c. 475 BC) was the first place where the word logos was given special attention in ancient Greek philosophy. In contrast to Heraclitus, Parmenides held that all is one and nothing changes. Zeno of Elea, a pupil of Parmenides, had the idea of a standard argument pattern found in the method of proof known as reductio ad absurdum. This is the technique of drawing an obviously false conclusion from an assumption, thus demonstrating that the assumption is false.
None of the surviving works of Plato (428–347 BC) include any formal logic, but they include important contributions to the field of philosophical logic. Plato raises three questions: What is it that can properly be called true or false? What is the nature of the connection between the assumptions of a valid argument and its conclusion? What is the nature of definition?
Aristotle and the Organon
The logic of Aristotle, and particularly his theory of the syllogism, has had an enormous influence on the history of logic and Western thought in general. Aristotle was the first logician to attempt a systematic analysis of logical syntax. He was the first formal logician, in that he demonstrated the principles of reasoning by employing variables to show the underlying logical form of an argument. He was the first to explicitly discuss the principles of non-contradiction and excluded middle.
His logical works, called the Organon, are the earliest formal study of logic that have come down to modern times. The probable order of writing of Aristotle’s logical works is: The Categories, a study of the ten kinds of primitive term; The Topics (with an appendix called On Sophistical Refutations), a discussion of dialectics; On Interpretation, an analysis of simple categorical propositions; The Prior Analytics, a formal analysis of what makes a syllogism; and The Posterior Analytics, a study of scientific demonstration. On Interpretation contains a comprehensive treatment of the notions of opposition and conversion; chapter 7 is at the origin of the square of opposition; chapter 9 contains the beginning of modal logic and the famous sea battle argument. The Prior Analytics contains his exposition of the syllogism, wherein three important advances are made for the first time in history: the use of variables, a purely formal treatment, and the use of an axiomatic system.
The Stoics
The other great school of Greek logic is that of the Stoics. Stoic logic traces its roots back to the late 5th century BC philosopher Euclid of Megara, a pupil of Socrates. The most important member of the school was Chrysippus (c. 278 – c. 206 BC), who was its third head, and who formalized much of Stoic doctrine. Three significant contributions of the Stoic school were their account of modality, their theory of the material conditional, and their account of meaning and truth.
Diodorus Cronus defined the possible as that which either is or will be, the impossible as what will not be true, and the contingent as that which either is already, or will be false. Diodorus is also famous for his Master argument. The first logicians to debate conditional statements were Diodorus and his pupil Philo of Megara. Philo regarded a conditional as true unless it has both a true antecedent and a false consequent. Philo’s criterion of truth is what would now be called a truth-functional definition of “if … then”; it is the definition used in modern logic. In contrast, Diodorus allowed the validity of conditionals only when the antecedent clause could never lead to an untrue conclusion.
The most important and striking difference between Megarian-Stoic logic and Aristotelian logic is that Megarian-Stoic logic concerns propositions, not terms, and is thus closer to modern propositional logic. The most original part of their theory is the idea that what is expressed by a sentence, called a lekton, is something real; this corresponds to what is now called a proposition.
Medieval Logic
The works of Al-Kindi, Al-Farabi, Avicenna, Al-Ghazali, Averroes and other Muslim logicians were based on Aristotelian logic and were important in communicating the ideas of the ancient world to the medieval West. Al-Farabi (873–950) was an Aristotelian logician who discussed the topics of future contingents, the number and relation of the categories, the relation between logic and grammar, and non-Aristotelian forms of inference. Ibn Sina (Avicenna) (980–1037) was the founder of Avicennian logic, which replaced Aristotelian logic as the dominant system of logic in the Islamic world. He developed an original “temporally modalized” syllogistic theory, involving temporal logic and modal logic. One of Avicenna’s ideas had a particularly important influence on Western logicians such as William of Ockham: Avicenna’s word for a meaning or notion (ma’na), was translated by the scholastic logicians as the Latin intentio; in medieval logic and epistemology, this is a sign in the mind that naturally represents a thing.
“Medieval logic” (also known as “Scholastic logic”) generally means the form of Aristotelian logic developed in medieval Europe throughout roughly the period 1200–1600. When the study of logic resumed after the Dark Ages, the main source was the work of the Christian philosopher Boethius. Until the twelfth century, the only works of Aristotle available in the West were the Categories, On Interpretation, and Boethius’s translation of the Isagoge of Porphyry. These works were known as the “Old Logic”. An important work in this tradition was the Logica Ingredientibus of Peter Abelard (1079–1142). The proof for the principle of explosion was first given by the 12th century French logician William of Soissons. By the early thirteenth century, the remaining works of Aristotle’s Organon had been recovered in the West, collectively known as the Logica Nova or “New Logic”. The period from the middle of the thirteenth to the middle of the fourteenth century was one of significant developments in logic, particularly in the theory of supposition.
