Philosophizing with a typewriter
This attempts to explain how Dasein's interests have a legitimate role in determining the being of entities within-the-world. This relationship between the latter entities and Dasein is best exemplified by those entities called equipment, so their being is considered and explained first. Also, Heidegger's ontology is partially contrasted with Descartes' and Heidegger's objections to the latter are summarized.
The being of tools is revealed in their function. Equipment, or tools, are entities that Dasein comports itself toward in concern. This concern is directed toward what makes a tool what it is, namely its being "something in-order-to...". In-order-to-ness involves as assignment or reference of something to something else. For example, when the task to be executed is to write an essay, a while constellation of equipment which function together is employed (assigned) to get the job done: the typewriter, paper, lamp, table, floor, room. The phenomenon of a tool always occurs in such a context, and it is in this context that a tool's being as a tool is best revealed. The being of a tool is not found in its being contemplated as a 'thing' (e.g., a typewriter) isolated from its context of equipment because this analysis misses the element which makes this 'thing' a tool- what Heidegger terms as "readiness-to-hand". Should the typist stop to ponder the typewriter's inner mechanisms, the machine's tool-ness, its function as equipment is no longer what is being manifested.
If a tool's being is its "readiness-to-hand", then what is the being of entities which are not tools? Are not all entities fundamentally present-at-hand, readiness-to-hand being a subset thereof? Heidegger says Dasein encounters all entities besides itself with a concern for its possible utilization, but that circumspection shows some entities are ill suited in one way or another to the task Dasein has in mind. This means that all entities within-the-world have a being which is both ready-to-hand and present-at-hand, but in some cases the entity is rendered unusable. As an example, a newborn colt is both present-at-hand and ready-to-hand. It is there, and it can be used for several things. If Dasein wants to use it as a pack horse, however, then the readiness-to-hand
...takes its farewell, as it were, in the conspicuousness of the unusable.
The glaring fact acknowledged by circumspection, that this colt must grow up first, overshadows the ready-to-hand of its being, but this kind of being does not therefore evaporate any more than turning off a lamp would diminish a painting's being according to the Cartesian ontology.
With these considerations the philosophical significance of tools becomes plain. The structure of being is a function of the references or assignments made. As it is Dasein which assigns, then Dasein's interests determine the structure of the being of entities present within-the-world. That is, this interest is a constitutive part of the world.
Such assertions directly oppose the traditional, Cartesian ontology, which maintains the real being of these present-at-hand entities is extension. This being of entities is a "substance" which depends on no other entity to be. Thus, Dasein's wants have nothing to do with what a present-at-hand entity is; such interests only make value judgments. For instance, Dasein determines a colt is unsuitable as a beast of burden because it is too young and weak to carry a bag of flour, but that in no way changes what a colt is, because according to this ontology a colt is its corporeal substance and nothing more. To give Dasein's interest any place in the real being of entities within the world is tantamount to abandoning the analysis of being, as it makes 'subjective' what is inherently 'objective'. Figuratively it is to put the philosopher's personal opinions and wishes before the facts about the horse.
Heidegger, however, has no qualms about putting Descartes before the horse. He argues that the Cartesian ontology never really settles the basic question of being, and that it even evades the question, holding it forever unanswerable. Also, by taking being to be some sort of permanent presence-at-hand, Descartes makes "...it impossible to lay bare any primordial ontological problematic of Dasein..." even though he claims to have adequately formulated and solved the problem of "the 'I' and the world". This ontology does not deliver what it promises, namely an account of what relation there is between 'I' and the world and what being is. Explaining the world as being composed of 'things' whose own being remains unclarified is not to address the question of what it means for these things to be, which is what is really being asked.
What is there, then, to bar Dasein from determining the being of entities within-the-world? The relation between Dasein and non-Dasein entities which Heidegger proposes is often condemned on the basis that it is "subjective". What this accusation means is that in such a relationship the world turns into a fantasy; Dasein need only change its mind and the world shall be flat again, or perhaps conical if that is more pleasing. What this criticism overlooks is that Dasein's interests and activities in the world are influenced by the world. That is, the world as matrix of human interests influences the interests by what it offers. Houses are built to shelter Dasein because of the cold and rain, and a pack horse is used because the burden is too heavy for Dasein to carry. Aside from this the world as something which is not Dasein is also brought into focus when Dasein pursues its interests but is thwarted. The horse is too weak, the typewriter keys stick, or there is a brick shortage. There is definitely a world Dasein must contend with, but the way entities within-the-world are referred or assigned to something, and hence their being in relation to one another, is left to Dasein. As an entity that cares, it is only Dasein that can undertake this ordering.
Heidegger shows that the being of tools is "ready-to-hand", and that this being is also applicable to entities considered to be merely present-at-hand. Since this way of being involves a reference made between entities, Dasein, being the only entity that concerns itself with the world and to make references, determines the being of all entities within-the-world.