Heidegger (H.) tells us we all have a pre-cognitive understanding of “being” already at work in our “everydayness”.  There are different ways that we relate to being.  For example, when we use a hammer to build something, we are relating to that hammer with a “pre-understanding” of its being.  We are relating to it in the mode of instrumentality.  In German, Heidegger refers to this as zuhanden, ready-to-hand.  In that mode, “being” shows itself as “disappearing in use”.  We relate to the being of the hammer as a “tool”.  If the hammer breaks while it is disappearing in use we immediately relate to it in another mode “present at hand”.  We look at it and say “stupid hammer” how dare you!  It becomes conspicuous, even a bit intrusive.  “Present at hand” is how science relates to being.  In this mode being is present as a thing (substance), an object of study, and shows itself to us.  In German, Heidegger refers to this as vorhanden, present-at-hand.  For H. when being is mis-understood (semblance) we relate to it in in-authenticity.  If we pre-understand our environment as instrumentality, we use it to accomplish a task such that it disappears in use, we use oil to make our cars go, we use trees to build our houses, etc. –  then, we pre-understand the being of nature/environment as “standing reserve”.  This is the problem of technology.  It comes from a confusion of how we relate to the being of “nature”, as a semblance of “nature”.  Why do I emphasize “nature””?  Because this shows something else about how we relate to being, we are historical beings.  We live in a “stretch” of time that goes from a past to a future not an instant present.  “Nature” is a term/relationship to a being that is carried with us from language, philosophy, history – metaphysics.  It tells us a pre-cognitive understanding of what something “is”, its being.  When what something “is” is a semblance we have failed to relate authentically with “it”.  The being of human (dasein) is what H. spends much of his effort on in Being and Time.  A few examples:   The experience of time – there is lived time and abstract, historical time.  Our history informs us that time is a series of abstract “now” moments and yet the way we live time is as a stretch.  When we are happy time seems/feels like it flies by quickly.  When we are depressed time drags on forever.  So the experience of time is different than the abstract notion of time as “now” moments.  Why do we privilege abstract time? – because we are historical beings and pre-understand time as an abstraction (i.e., a history defined by “now” moments) – this informs us about time – not how we experience it.  Another example:  The experience of space – history tells us that space is linear extension, “things” are x number of feet away in 3 dimensional space…but what about lived space?  – When I am looking at a glass of water while wearing glasses the glasses on my face is closer to me in terms of linear extension but in a lived sense I am closer to the glass of water, I am together with the glass of water, co-habiting its space.  So humans can de-sever regions of space and bring them close or far at will.  If I am walking down a hallway I am not calculating the feet to all the walls, floor and ceiling (as perhaps a robot would do) to orient myself, to keep from falling.  In a lived sense, I am co-habiting the region of the hallway and orienting myself accordingly.  Again, we privilege the abstract over the lived (phenomenological) experience because we are historical beings.  This is a short intro. into H. and his work.  It gets better!