Consciousness is a state where objects (mental or otherwise) are conscious. I am conscious. I believe this is true because the experience of consciousness is one that I an conscious of. In other words, I am aware of my awareness of objects, so I assume that awareness is a property I hold. Perhaps you are conscious as well.
I have direct access to my consciousness (I am aware of my awareness), but I cannot observe the consciousness of others. I can observe behaviors that other animals exhibit. If those behaviors are like my own, especially on ones that I believe involve my consciousness, I may assume that they have consciousness as well.
However, I am not sure if any of my behaviors involve my consciousness causally, or if my conscious experience is simply an artifact of nonconscious operations. Perhaps my consciousness is epiphenomenal. My thoughts are a byproduct, my intentions are inconsequential.
Because of this, the properly skeptical point of view is to assume that no behaviors require consciousness, and that no animals possess the property of consciousness.
I can, of course, quibble with the definition of consciousness. But I don't want to get into semantics. I'm over my character limit.