It is then perhaps an odd juxtaposition that we would turn precisely to Heidegger for words about that subdivision of philosophy to which he seems least attached: logic. Yet, as every philosopher must, he busied himself, at least for some fraction of his time, with logic. In his lecture notes for the 1925/1926 academic year, he wrote:
If we desire a more vital concept of “logic,” we have to ask a more penetrating question: what is the subject matter of the science of logic? In doing so, we leave aside any consideration of logic as one discipline among others - viz., the science of speaking and therefore of language - and focus instead on what it is about.
Heidegger here uses the word ‘science’ in the philosophical sense: in ordinary life, we think of ‘science’ as biology and chemistry, as geology and astronomy. The philosophical sense is broader, including those, but including also anything which can be made into a systematic body of knowledge, or an academic discipline. Not only is the philosophical sense of the word broader, but it carries a different emphasis: it is not the content of biology or astronomy (frogs and stars, respectively) which interests the philosopher, but rather the systematic arrangement of that content - that it can be categorized according to a taxonomy, or its events analyzed in terms of cause and effect. It was a philosopher, Aristotle, who organized not only a taxonomy for biology, but for political science and other fields as well.
It is in this sense, then, that Heidgger speaks of ‘the science of logic’ - and here also he is following a philosophical tradition; the very phrase ‘science of logic’ (die Wissenschaft der Logik) has a long and venerable history among philosophers.
Seen historically, Heidegger proposes that logic arose from the study of language (grammar), and the study of language arose from the study of speaking. After sketching his somewhat obscure distinction between ‘language’ and ‘speaking’ - the latter being the most literal study of making sounds with the mouth, and the former a somewhat more abstract study of meaning and grammar - he goes on to explain logic as an extrapolation from speaking and language: what the speaking is about, or what the language is about:
the basic achievement of speech consists in showing or revealing what one is speaking about, what one is discussing. Indeed, making vocal sounds was quite secondary to that.
As one abstracts from speech and language to logic, we see that grammar is to language as logic is to thought: and it is in thougt that the content of the “science” at hand will be defined and revealed:
In such acts of revealing, whatever one is speaking about shows up, becomes perceivable, and, as something perceived, get defined in and by the discussion about it. This revelatory defining of what is experienced and perceived is the very same thing that we generally call “thought” and “reflection”.
To speak of a process of ‘revealing’ is typically Heideggerian, for which he is alternately loved and hated. Heidegger’s concept of ‘truth’ is a notion of uncovering or disclosing, which stands in contrast to a competing concept, truth as corresponding. In a correspondence view of truth, symbols - be they spoken or written, be they mathematic, scientific, or ordinary words - are true if they are arranged in a patterns which corresponds to reality. Heidegger, to the contrary, embraces his own view of truth, that it consists in, not corresponding to reality, but rather revealing or disclosing it. Heidegger goes on:
In summary: in our primary, natural experience of how human beings live together with each other, we understand speech as the revealing of something by speaking about it, and as a thinking that determines and orders it. Language, speaking, thinking: they coincide as the human way of being. They are the way we reveal and illumine (both for ourselves and for others) the world and our won human existence, so that in this luminosity we gain sight: human insight into ourselves and an outlook on, and a practical insight into, the world. Logic as the science of speaking, studies speech in terms of what it properly is: the revealing of something. The subject matter of logic is speech viewed with regard to its basic meaning, namely, allowing the world, human existence, and things in general to be seen.
The subject matter of logic is not merely speech, but speech viewed viewed with regard to its basic meaning. Grammar, philology, and related disciplines are the study of speech; logic is the study of speech’s meaning. Phrased another way, logic is ‘deep grammar’, while the ordinary study of phonemes and morphemes is ‘surface grammar’. Because deep grammar is deep, it needs to be uncovered, discovered, and revealed:
The fact that existence has and understands and strives for this basic form of revealing implies that, for the most part, much of the world stands in need of ‘revelation’, of being uncovered and made known. In other words, much of the world and much of human existence is by and large not un-covered. So beings can be drawn out of their not-un-covered-ness, their hiddenness. They can be un-covered or un-hidden. This uncoveredness or unhiddenness of beings is what we call truth.
Following Aristotle (who followed Socrates), Heidegger sees definitions as central to logic:
Logic investigates speaking - the thinking that defines things - inasmuch as speaking uncovers things. The topic of logic is speech, specifically with regard to truth.
Observational sciences, natural sciences, like chemistry or biology, are also concerned with truth. Likewise, social sciences like sociology or political sciences seek truths. So what makes logic different, or even distinct, from them? Those other sciences seek to identify truths, or to sort out which statements are true and which are false. Logic, according to Heidegger, takes true statements and asks why they are true and how they are true.
Our definition of logic as the science of truth could be misunderstood. One might object that every science deals with truth, that truth is what all scientific knowledge is after. Yes, except that there is a misleading ambiguity here in how the word truth is being used. In a strict sense, no individual science other than logic deals with truth. The natural sciences, on the other hand, deal only and always with the true, i.e., what-is-true; and they do so within the arena of the knowledge of nature. Or outside of the natural sciences, one inquires into what-is-true for human action, or about the true that faith gives.
Logic deals with truths; the concrete individual sciences deal with truths. There are biological truths, spiritual truths, geological truths, ethical truths; but logic deals with truth itself, truth seen as truth, not seen in relation to the content of a particular science. Astronomy gives us truths; faith gives us truths; chemistry gives us truths; morals give us truths; but logic examines truth itself - what it is to be true.
But logic does not ask about the what-is-true in just any sense. Rather, it inquires primarily and properly into the truth of what-is-true. It asks: What makes this or that true thing be true in a given case? and what makes it be this true thing? The only way to make any grounded sense out of the truth of theoretical-scientific knowledge, practical reflection, or religious truth is to get to the foundation that lets us understand what truth means at all. Only from that foundation can we decide which kind of truth is most original, and whether the ideal of truth is to be found in theoretical-scientific truth or practical insight or religious faith. In other words, it is not easily decided which form of the true is primary and most basic. Even in today’s philosophy, this question has not yet been settled.
Heidegger indicates that we should seek which form of truth is most ‘primary’ and ‘basic’ - this will be a daunting task, for it is not clear which standards will allow us to judge in this case, and it is perhaps a bit too optimistic to assume that philosophers as a community will ever agree to any potential answer.
