Logical Investigations

Logical Investigations (1900–1901)

Author: Edmund Husserl · Volume 1 (Prolegomena): 1900 · Volume 2 (Six Investigations): 1901 Logische Untersuchungen

The Argument in One Paragraph

Logic is not a branch of psychology. Its laws are not contingent generalizations about how the human mind happens to work; they are a priori, necessary, and binding on any rational being whatsoever. The first volume — the Prolegomena to Pure Logic — proves this negatively, by demolishing the then-fashionable doctrine of “psychologism” and showing that any attempt to reduce logical laws to psychological ones produces a self-refuting “skeptical relativism.” The second volume — six dense Investigations — turns from logic to consciousness and supplies the positive groundwork for a new science: a rigorous descriptive analysis of how the mind grasps ideal objects (meanings, propositions, numbers) through intentional acts that are essentially directed at something. Along the way, the book founds a formal ontology of parts and wholes, projects a “pure logical grammar” of the a priori laws governing the combination of meanings, and reformulates Brentano’s intentionality with the rigor of a mathematician. Its motto — “Wir wollen auf die ‘Sachen selbst’ zurückgehen,” “We must go back to the things themselves” — became the slogan of the entire phenomenological movement.

---

What the Book Is About

The Logical Investigations are Husserl’s breakthrough — the work that turned a Halle mathematics professor into the founder of a philosophical movement. Trained as a mathematician under Weierstrass and Kronecker, drawn into philosophy by Brentano, Husserl had spent the 1890s working on the foundations of arithmetic and finding himself unable to ground them inside the psychologistic framework his earlier Philosophy of Arithmetic had assumed. The Investigations are the result: a two-volume, thousand-page act of self-correction and re-foundation that takes apart the inherited picture of logic-as-psychology and builds, in its place, the first sustained phenomenological description of intentional consciousness.

Volume 1 — the Prolegomena to Pure Logic. This is the polemical volume, and the one that made Husserl’s reputation. Its target is psychologism: the view, common from John Stuart Mill through Sigwart and Erdmann, that logical laws are really laws of how the human mind thinks. Husserl’s refutation has the quality of a reductio. Psychological laws, like all empirical laws, are inductive, contingent, only “probable.” Logical laws — the law of contradiction, modus ponens, the laws governing valid syllogism — are a priori, certain, necessary. To reduce the latter to the former is a category mistake, and one with a self-refuting consequence: if the law of contradiction were merely an empirical generalization about Homo sapiens, then some other species, or some future state of our own, could violate it without inconsistency, which would mean the law was never necessarily true to begin with. “The correctness of the theory presupposes the irrationality of its premises, the correctness of the premises the irrationality of the theory” (§26). The result is “skeptical relativism,” and Husserl argues that any honest psychologist who follows their position to its conclusion arrives there. “Truths are what they are, whether they are grasped by men… or not” (§65). Logic deals with ideal objects — meanings, propositions, numbers — and the laws governing them are timeless, not biological.

What is logic, then, if not psychology? Husserl’s answer, taking up Bolzano’s old project, is that logic is a Wissenschaftslehre — a “theory of science.” It is the science of what makes any science possible at all: the formal-ideal conditions of any objective unity of theory whatsoever. Numbers, propositions, and the logical relations among them are ideal objects of a different category from psychological events. “The number Five is not my own or anyone else’s counting of five, it is also not my presentation or anyone else’s presentation of five” (§46). The single most important methodological lineage Husserl claims here is to Bolzano: “Logic as a science must… be built upon Bolzano’s work, and must learn from him its need for mathematical acuteness in distinctions, for mathematical exactness in theories” (§61).

Volume 2 — the Six Investigations. The second volume is what made the book a founding text of phenomenology rather than just an anti-psychologistic polemic. The six Investigations turn from the ideal objects of logic to the conscious acts through which those ideal objects are grasped, and they supply, in extraordinary descriptive detail, the positive science Volume 1 had only cleared the ground for. The volume opens with the motto that became the discipline’s first commandment: “Wir wollen auf die ‘Sachen selbst’ zurückgehen” — “We must go back to the things themselves.” No more inherited theories, no more speculative constructions; describe how the matter actually shows up to consciousness.

Investigation I — Expression and Meaning. The opening Investigation distinguishes the expression (an Ausdruck, a sign endowed with a sense) from the merely indicative sign (the smoke that indicates fire). It then introduces the crucial distinction between the act of meaning (a psychological event in time) and the meaning itself, “the ideal unity of meaning as against the multiplicity of acts” (§11). When you and I both think “two plus two equals four,” the same ideal proposition is grasped in two different acts. The act is real and temporal; the meaning is ideal and timeless. Conflating them is the original sin of psychologism.

Investigation II — The Universal Object (Species). Husserl defends the existence of universals — what he calls Species — against the nominalism of Locke, Berkeley, and Hume. Locke’s “general idea of a triangle” (an image that is somehow neither right-angled nor obtuse nor acute) is dispatched as “a psychological monstrosity” (§11). Universals are real, but as objects of a different category from individuals: “We mean the red, not the red house; the species, not the individual” (§1).

Investigation III — The Theory of Wholes and Parts. This is the strange, brilliant Investigation that founds formal ontology — the a priori science of the structures of any object whatsoever. Husserl distinguishes two kinds of parts: Stücke (“pieces”), which are independent and can exist separately from the whole (a leg can be cut from a body), and Momente (“moments”), which are non-independent and require foundation (Fundierung) in something else to exist at all (a color requires extension; an extension requires a colored surface). The relation of Fundierung — “if a part A cannot exist without a part B existing” — is an a priori law of essence, not an empirical generalization. The mereology developed here will turn out to underlie everything from the logic of meanings (Investigation IV) to the structure of intentional acts (Investigation V) to the late phenomenological analysis of perception.

Investigation IV — Pure Logical Grammar. Husserl projects mereology onto meanings. Some meanings (nouns, complete propositions) are categorematic — independent, able to stand alone. Others — “and,” “but,” “if” — are syncategorematic — non-independent moments that require a categorematic foundation to enter a unified sense. There are a priori laws governing how meanings can combine, and these laws “divide sense from nonsense” (Introduction). The boundary between the senseless (ungrammatical word-strings) and the absurd (logically contradictory but grammatically well-formed) is itself an a priori boundary. This is the Idea of a Pure Logical Grammar, and it has fingerprints all over twentieth-century formal semantics and structural linguistics.

Investigation V — Intentional Experiences. The decisive Investigation, and the one Heidegger would later call the “discovery” of phenomenology. Husserl reformulates Brentano’s intentionality with new precision. Every conscious act is “directed” at an object: “In perception something is perceived, in imagination something imagined” (§10). But — and this is the move that breaks the modern picture — the intentional object is not a real part of the act. “The God Jupiter is not a real constituent of the experience” of thinking about Jupiter (§11). When I think of Jupiter, there is no little Jupiter inside my head. The “image theory” — consciousness as a “box-within-box structure of conscious contents” — is dismissed in one of Husserl’s most famous polemics. Consciousness has its objects, but it has them by meaning them, not by containing them. He distinguishes the reell content of the act (the actual sensations, act-characters lived through) from the intentional object the act is directed at, and within the act itself he distinguishes its quality (perception vs. memory vs. imagination — the “how” of the act) from its matter (what it is directed at — the “what”). Together, quality and matter form the “intentional essence” of the act. He also identifies a particular act-type — the objectifying act — as the foundational layer underlying every other kind of act: every feeling, every wish, every judgment is founded on a presentation of an object. You cannot fear nothing; the fear is founded on a presentation of the feared.

Investigation VI — Categorial Intuition and the Phenomenology of Knowledge. The climax. Husserl introduces kategoriale Anschauung — “categorial intuition” — the higher-order intuition through which we directly grasp logical forms and states of affairs, not just sensible particulars. We don’t only see the apple is red; we see that the apple is red — and the that-structure is itself given. This is how the mind moves from “empty” symbolic thinking to the fulfilled grasp of objective truth. The Investigation is the conceptual bridge from logic back to phenomenology: science is possible because there is an essential correlation between subjective intentional acts and the ideal, law-governed objects they make accessible.

Key Concepts

• Psychologism. The doctrine — Mill, Sigwart, Erdmann — that the laws of logic are really empirical laws of human thinking. Demolished in the Prolegomena.
• Wissenschaftslehre (Theory of Science). Bolzano’s term, taken over: logic as the science of what makes any science possible — the a priori conditions of the unity of theory.
• Ideal objects / Species. Meanings, propositions, numbers, universals — timeless and law-governed, of a different ontological category from psychological events. “Truths are what they are, whether they are grasped by men or not.”
• Expression vs. indication. The Ausdruck is a sign endowed with meaning; the indicative sign (smoke for fire) functions through a blind associative link. Phenomenology is interested only in expressions.
• The ideal unity of meaning. “The ideal unity of meaning as against the multiplicity of acts” (Inv. I §11). Different acts can grasp the same meaning; the meaning is one, the acts many.
• Stück / Moment / Fundierung. Independent piece vs. non-independent moment; the a priori relation of foundation through which non-independent parts are bound to their wholes. The basis of formal ontology (Inv. III).
• Pure logical grammar. The a priori laws governing how meanings combine. Categorematic vs. syncategorematic expressions; the distinction between the senseless and the absurd (Inv. IV).
• Intentionality. Consciousness as essentially directed at an object. “In perception something is perceived, in imagination something imagined.” The intentional object is not a real part of the act.
• Reell content vs. intentional object. What is really in the act (sensations, act-characters) vs. what the act is directed at. The distinction that kills the image theory.
• Quality and matter of an act. The “how” of the act (perceiving, remembering, imagining) vs. the “what” (what it’s directed at). Together: the intentional essence.
• Objectifying acts. The foundational layer: every feeling, wishing, willing is founded on an act of presentation of an object.
• Kategoriale Anschauung (categorial intuition). The higher-order intuition through which logical forms and states of affairs are directly given (Inv. VI). The bridge from sensible perception to logical truth.
• Die Sachen selbst. “The things themselves.” The motto of the second volume and of phenomenology as a movement.

Key Quotations

1. “We must go back to the ‘things themselves.‘” — Vol. II Introduction. The motto.
2. “Truths are what they are, whether they are grasped by men or not.” — Prol. §65. The ideality of truth.
3. “The number Five is not my own or anyone else’s counting of five, it is also not my presentation or anyone else’s presentation of five.” — Prol. §46. The ideality of mathematical objects.
4. “The correctness of the theory presupposes the irrationality of its premises.” — Prol. §26. The self-refutation of psychologism.
5. “Logic as a science must… be built upon Bolzano’s work.” — Prol. §61. The lineage Husserl claims.
6. “The ideal unity of meaning as against the multiplicity of acts.” — Inv. I §11. The foundational distinction.
7. “Locke’s universal triangle… is a psychological monstrosity.” — Inv. II §11. The dispatch of nominalism.
8. “Evidently this is no mere empirical fact, but an a priori necessity, grounded in pure essence.” — Inv. III §4. The signature move from fact to essence.
9. “In perception something is perceived, in imagination something imagined.” — Inv. V §10. Intentionality in one sentence.
10. “The God Jupiter is not a real constituent of the experience.” — Inv. V §11. The death of the image theory.
11. “We do not see color-sensations but colored things.” — Inv. V, Appendix to §11. Against phenomenalism.
12. “Every act is founded on an act of presentation.” — Inv. V §32. The priority of objectifying acts.

How It’s Written

A “systematically bound chain of investigations,” not a finished system — Husserl’s own description. The Prolegomena is polemical, fast, exhilarating: the writing of someone who has finally seen through a long-standing confusion and is taking it apart in public. The six Investigations are slower, denser, sometimes serpentine, with what Husserl himself called a zig-zag method: move forward into a logical result, then circle back to the act that produces it, then forward again at greater depth. The reader must do the same. The book repays patience the way a long mathematical proof does, and it broke Husserl’s career open with first-rate mathematicians and philosophers (Frege exchanged letters with him; Heidegger said that Investigation VI was “the first time philosophy had ever taught me how to read”; the Munich and Göttingen schools formed around it within a decade of publication).

Connections

• Husserl — the breakthrough. Without the Logical Investigations, no phenomenology. Without the second volume, no Ideas I.
• Ideas I — the radicalization. Ideas I takes the analysis of intentional acts in Investigation V and lifts it onto transcendental ground via the epochē. The early Göttingen students who loved this book never followed Husserl into that radicalization.
• The Crisis of European Sciences — the late return. The Crisis tells the historical story behind the demolition of psychologism: how the modern sciences came to need an analysis of subjectivity in the first place, and why phenomenology had to be invented.
• Kant — the distant ancestor. The project of grounding the sciences in a priori structures is Kantian; the descriptive method is Husserl’s own.
• Brentano — the immediate teacher. Brentano’s Psychology from an Empirical Standpoint (1874) had introduced intentionality. Husserl honors him and breaks with him: Brentano had stayed inside descriptive psychology and treated intentional objects as somehow contained in the mind. Investigation V’s “the God Jupiter is not a real constituent of the experience” is an explicit correction.
• Bolzano. The lineage Husserl claims for “pure logic” — an unfashionable nineteenth-century logician whose Wissenschaftslehre (1837) had already insisted on the ideality of propositions and truths.
• Frege. The parallel anti-psychologistic move. Frege and Husserl independently demolished the same target around 1900; their methods diverged afterward, and the divergence is one origin point of the analytic–continental split.
• Heidegger. The most consequential reader. Being and Time is unimaginable without Investigation VI’s categorial intuition and Investigation III’s mereology of Fundierung; the existential analytic of Dasein is post-Husserlian phenomenology in Heidegger’s idiom.
• Sartre — Sartre’s appropriation of Husserl runs through Investigation V’s account of intentionality without the transcendental ego of Ideas I. The Transcendence of the Ego (1937) is essentially an attempt to read the Investigations against Ideas.
• Edith Stein, Roman Ingarden, Reinach — the Munich-Göttingen “realist” phenomenologists, all formed by this book and never reconciled to Ideas I’s transcendental turn.
• Analytic philosophy. The Prolegomena’s critique of psychologism is part of the same wave that produces Frege, early Russell, and later the sharp logic-vs-psychology distinction in twentieth-century analytic work.

Lineage

• Predecessors: Bolzano (theory of science, ideal propositions); Lotze (the ideality of meaning); Brentano (intentionality, descriptive psychology); the mathematical tradition (Weierstrass, Cantor) for the model of rigor; Frege (anti-psychologism, parallel and partly overlapping); Locke, Berkeley, Hume (the nominalist target dismantled in Investigation II).
• Successors: Ideas I (1913) and the rest of Husserl’s transcendental work; Heidegger (categorial intuition transposed into the analytic of Dasein); the Munich and Göttingen schools (Reinach, Stein, Ingarden, Conrad-Martius — the realist phenomenologists); Sartre (intentionality without the transcendental ego); Merleau-Ponty (phenomenology of perception); Levinas (ethics as first phenomenology); Derrida (whose engagement with Husserl begins with the Investigations); twentieth-century formal semantics and the project of a “logical grammar.”