The Thing
Analysis of the machine led Duchamp to another particularly important perspective effect. As a matter of fact, it is quite possible to describe a ready-made as a modification of the perspective associated with an object.  

The perspective associated with an object (with a man-made object, I mean) is the angle from which it is usually seen. That is to say, its purpose, its goal, its usage  
Just like the classical perspective, this is essentially a trap.  

We have come to the point of only seing in things what we have predicted and decideed that they would be. And most of the time, we tend to stay stuck there, fascinated as we are by the unreasonable efficiency of machines. Actually, it must be admitted that they do quite exactly what we have predicted that they would. But in general this impression results from a rather short sighted sort of vision. Usage of tools and machines has also long term or hidden consequences which tends to escape out of the reach of our mental abilities during quite long periods of time. The accumulation of some large scope ecological problems shows clearly enough that restricting our vision of things to the sole perspective of their predicted usage is a very dangerous sort blindness, which threatens not only our lives but also Life as such.  

But there is worse. Because since quite a long time ago now we mostly have around us these objects, tools, machines that we built, we have come to the point of casting our specifically technical "What for ?" type of questionning in all directions, in lots of domains in which it has nothing to do, in which it may not be assigned any definable meaning at all. We understand quite easily that it is not reasonable to grant feelings and emotions to machines, but we do not understand that well that it is just as ridiculous to grant a purpose to entities such as the sun, the universe, a grain of sand, a giraffe, Life.  
It is not more serious to wonder "why" (what for) there are elephants, mountains, rivers, viruses, galaxies than to ponder over the electrical charge of jealousy or the temperature of a prime number. Nature is not there for any purpose, it is not there for a goal, it is not there to fulfil a technical nor utilitarian prediction.  
"Nature takes place, no one will add to it" said Paul Valery. It may be.   

Quite a few people realize that only man-made objects may have a purpose. This blindness has reached such a point that most men have since long come to feel uncomplete not to have a purpose too. And they are still left weeping on the death of this god who granted them the gift to take themselves for his things. And they are claiming or allowing anyone to claim for them on all information media that they want to be given goals, values, usage. And they are begging everywhere that someone may be good enough to give a purpose to their lives. And they are longing so hard to be things, that they even die of it. They suicide in numbers whenever they get the feeling that their lives do not have a purpose.  

We might have dreamt a god that grows, a vegetal god, or a crystal god, a dreaming god, an infinitely lazy god that would do nothing, nothing at all. But that is actually not what happened. We dreamt a creator god, a deus ex machina, a potter god kneading our bodies out of clay just as we knead and love and cherish our things. But our bodies are history, but our bodies by the most radical quality of freedom, simply happen. For no purpose.  

And although god is dead now, we just stayed stuck there. We remained things, things to each others and to ourselves. So that it is said that objectivity is a quality, a virtue. But even our passions are certainly not unscathed, since the thing whispered to us our objects of desire and our sexual objects. Which created the entire SM galaxy of which we all more or less partake. How would human love look like if the thing had not come to meddle with our deepest and most intimate feelings and sensations ? That is what future generations only shall be able to explore - if anything like a decontamination ever proves to be possible.  

"People living in the age of machine are naturally influenced, consciously or unconsciously by the age in which they live. I think that I was conscious enough when I introduced derision if this holy era. Humour and laughter - not necessarily disparagement - are my favorite tools" [1]   

Indeed machines and instruments do not laugh. And this absence of laughter shows the track of anything specifically  inhuman they apply on anything human. Any group or individual that will understand the implication of the remarks above shall be confronted with the necessity of using this absence of laughter as a sure criteria, a compass. What does not laugh partake of the instrument.   

"Reverse ready-made - use a Rembrandt as ironing board"  

Perched on top of his ready mades, Duchamp sees the totality of Art, as it was still meant and understood at the beginning of Renaissance, in all its narrowness of mind. Not only Fine Arts about the sclerosis and narrowness of which he never had any doubts, and with which he definitely broke in 1912, but all Arts. That is to say Fine Arts as well as Arts that are not that fine, as well as the various scientific, technical, industrial, and craftsmanship specialities.   

Out of this vision comes this fanstastic call back to the order of reality and this sincere honour done to Leonardo Da Vinci in 1919: "LHOOQ". The cunt of reality is warm.

[1] - "La mariée mise à ni chez Marcel Duchamp même" - Arturo Schwarz - P29