Martin Heidegger, best known for his seminal work Being and Time, was the german philosopher who attempted “to work out the question of the sense of being and to do so concretely.” Many would say he succeeded.
In Being and Time, Heidegger sets out to establish concretely three modes of being. The first mode of being, Dasein, is the mode of being of humans. This mode is characterized by having a stance on the question of being i.e. making being an issue. By this, Heidegger means that humans, whether they know it consciously or not, take a stand on their own being by having particular roles that they fall into holistically, such as “being a mother” or “being a teacher”. These roles cannot be defined outside of the contextual, existential matrix that is formed through communal activity.
The next two modes of being are presence-at-hand and readiness-to-hand. The latter can be characterized as the mode of being of human equipment. According to Heidegger, equipment has a mode of being because you can’t separate a tool from the holistic environment of its usage. He uses the example of a hammer. You can’t properly talk about hammers outside of the entire contextual matrix of nails and other equipment related to the act of hammering. Entities that do not have readiness-to-hand and are not Dasein are present-at-hand, meaning that they are “just there” in the environment.
Heidegger’s task in Being and Time was to take beings and their being seriously. If you are interested in learning more about Heidegger, Hubert Dreyfus, who I talked about two posts ago, has posted his entire Fall 2007 Heidegger lectures online. I highly recommend them.