What is consciousness?

Do you reckon this fly is conscious? I don't know...but I do know that we are on shaky ground trying to answer the question until we are crystal clear about what we mean by consciousness. So for this first post I have gathered together some definitions of consciousness and what it means to be conscious.

Collins English Dictionary

Conscious: 1. a. alert and awake; not sleeping or comatose; b. aware of one's surroundings, one's own thoughts and motivations, etc. 2. aware of and giving value or emphasis to a particular fact or phenomen. 3. done with full awareness; deliberate. 4. denoting or relating to a part of the human mind that is aware of a person's self, environment and mental activity and that to a certain extent determines his choices of action.

Roger Penrose in The Emperor's New Mind (1989) (quoted in The Oxford Dictionary of Thematic Quotations)

Consciousness...is the phenomenon whereby the universe's very existence is made known.

William James (1842-1910) defined consciousness as the "function of knowing". He considered consciousness a tool which, by its nature, is selective, fluid, and personal- a tool founded upon logic which serves to create an inner coherent reality.

Thatcher and John, 1977, p. 294 (quoted in The Oxford Companion to the Mind)

Consciousness: a process in which information about multiple individual modalities of sensation and perception is combined into a unified multidimensional representation of the state of the system and its environment, and integrated with information about memories and the needs of the organism, generating emotional reactions and programs of behavior to adjust the organism to its environment...

My own definition in The Mechanisms of Consciousness (2017):

To be conscious of something is to know that we know it. Therefore to understand consciousness, it is sufficient to define what it is to know something.

To know something is to have instantiated in our mind a mental structure that enables us to pay attention to significant inputs, discriminate different values of those inputs, and produce useful outputs in order to give us control relative to that thing.

Therefore to know that we know something (i.e. to be conscious of it) is to have instantiated in our mind a second mental structure that enables us to pay attention to the first mental structure, and produce outputs that give us control relative to it.