I'm confused about two things:

1) Does crossing the boundary imply stepping INTO or stepping OUT OF the bounded area or idea?

For example:

Never cross the boundaries of freedom of expression


Never cross the boundaries of immorality

2) When should I pluralize boundary? For example, should I pluralize it in "crossing the boundary/boundaries of the system"?

  • 2
    We normally use the plural boundaries, but note that it's not normal to speak of crossing the boundaries of immorality (only 24 results in Google Books there). We usually refer to the boundaries of morality (8490 results). It's entirely a matter of context/logic/semantics whether you're going into or out of the bounded entity. Jul 30, 2013 at 0:57
  • Whether you are going into or out depends completely on the type of sentence in which it is used. Jul 30, 2013 at 7:36

1 Answer 1


1) Crossing the boundary of something can mean either direction: into or out of. It depends on the surrounding text. In either case, it usually means that the person crossing the boundary is doing something unexpected and they probably shouldn't be doing it. The boundary is there for a reason, so crossing it is significant in either direction.

2) Boundary is sufficient when you are discussing one particular boundary: the edge of the football field is the boundary for where players may stay. If this particular line is crossed, you could say the player crossed the boundary.
Use boundaries for the more abstract ideas, like the morality and freedom of expression that you mention in the question. They don't have a particular, physical line for you to cross.

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