Comics are essentially: imagery (non-specific), and words (but not necessarily, and not forgetting that words are also images), arranged in a linear sequence to tell a story (non-specific, and in the digital realm, “linear” is up for grabs as well). That’s all. No mention of ink and line, word balloons, etc. These things don’t define comics, they are ticks and mannerisms you can use or lose, like “the fade out,” “the voice over,” “the jump cut” in film.
Other quotes from Dave McKean.