I found McCloud's dissection of comics, in an attempt to discern a definition, very interesting.
I'm taking a philosophy class right now that is about how we define things.
Many definitions are accurate, but are vague enough to encompass other distinct items.
Others only apply to the concept in question, but abstract the concept until it is meaningless.
You can break comics down into physical components, ink and paper, but then you lose the content and experience of reading them.
Defining anything philophically is difficult but an art medium even more so than others.
One point McCloud proposes is that, by depicting figures with a cartoon art style, you make them more universal. I cannot recognize myself in a highly detailed renaissance portrait, but I, and everyone else, recognize that I match this simplified figure. We are all able to identify outselves with a smiley face, while only one can match a photo. This made me think of emojis, and their popularity. Though miscommunications are definitely possible, they are often more efficient than text to convey emotiion because they match the face we make as we type. These simplified cartoons have become a standard in digital communication to make up for how you can't see the speaker over text.