Example: "There is no clear division between a liquid and a solid. The soggy soil we are standing on is a case in point. So is the yogurt you're having."
What's an idiom, phrase, or word for "no clear division"?
I thought of "fine line", but it doesn't seem to be appropriate in this case; a "fine line" is usually used in a cautionary way, with the second object being unfavorable in some way - for example, "There is a fine line between being funny and being immature."