And because the function of the λόγος lies in merely letting something be seen, in letting entities be perceived [im Vernehmenlassen des Seienden], λόγος can signify the reason [Vernunft]. And because, moreover, λόγος is used not only with the signification of λέγειν but also with that of λεγόμενον (that which is exhibited, as such), and because the latter is nothing else than the ὑποκείμενον which, as present-at-hand, already lies at the bottom [zum Grunde] of any procedure of addressing oneself to it or discussing it, λόγος qua λεγόμενον means the ground, the ratio. And finally, because λόγος as λεγόμενον can also signify that which, as something to which one addresses oneself, becomes visible in its relation to something in its 'relatedness', λόγος acquires the signification of relation and relationship.1
This Interpretation of 'apophantical discourse' may suffice to clarify the primary function of the λόγος.
C. The Preliminary Conception of Phenomenology
When we envisage concretely what we have set forth in our Interpretation of 'phenomenon' and 'logos', we are struck by an inner relationship between the things meant by these terms. The expression "phenomenology" may be formulated in Greek as λέγειν τὰ φαίνομενα, where λέγειν means ἀποφαίνεσθαι. Thus "phenomenology" means ἀποφαίνεσθαι, τὰ φαίνομενα—to let that which shows itself be seen from itself in the very way in which it shows itself from itself. This is the formal meaning of that branch of research which calls itself "phenomenology". But here we are expressing nothing else than the maxim formulated above: 'To the things themselves!'
Thus the term "phenomenology" is quite different in its meaning from expressions such as "theology" and the like. Those terms designate the objects of their respective sciences according to the subject-matter which they comprise at the time [in ihrer jeweiligen Sachhaltigkeit].
1 Heidegger is here pointing out that the word λόγος is etymologically akin to the verb λέγειν, which has among its numerous meanings those of laying out, exhibiting, setting forth, recounting, telling a tale, making a statement. Thus λόγος as λέγειν can be thought of as the faculty of 'reason' ('Vernunft') which makes such activities possible. But λόγος can also mean τὸ λεγόμενον (that which is laid out, exhibited, set forth, told); in this sense it is the underlying subject matter (τὸ ὑποκείμενον) to which one addresses oneself and which one discusses ('Ansprechen und Besprechen'); as such it lies 'at the bottom' ('zum Grunde') of what is exhibited or told, and is thus the 'ground' or 'reason' ('Grund') for telling it. But when something is exhibited or told, it is exhibited in its relatedness ('in seiner Bezogenheit'); and in this way λόγος as λεγόμενον comes to stand for just such a relation or relationship ('Beziehung und Verhältnis'). The three senses here distinguished correspond to three senses of the Latin 'ratio', by which λόγος was traditionally translated, though Heidegger explicitly calls attention to only one of these. Notice that 'Beziehung' (which we translate as 'relation') can also be used in some contexts where 'Ansprechen' (our 'addressing oneself') would be equally appropriate! Notice further that 'Verhältnis' (our 'relationship'), which is ordinarily a synonym for 'Beziehung', can, like λόγος and 'ratio', also refer to the special kind of relationship which one finds in a mathematical proportion. The etymological connection between 'Vernehmen' and 'Vernunft' should also be noted.
Sein und Zeit p. 34