Refers to literal obstruction like walls, shields, or natural barriers that can't be passed through.

Physical Barrier

Often used to describe high-level security measures or materials that cannot easily be compromised.

Security

Used metaphorically to imply something is very strong, it often relates to strength or resilience.

Metaphoric Use

Indicates that a topic or text is challenging to understand due to its complexity or lack of clarity.

Intellectual Challenge

Often associated with complex theories or ideas in academic fields such as philosophy or physics.

Abstract Concepts

Describes a person's thoughts or feelings that are difficult to understand or empathize with.

Emotional Distance

 It's therefore useful for our brains to construct notions like "solidity" and "impenetrability," because such notions help us to navigate our bodies through the middle-sized world in which we have to navigate. Moving to the other end of the scale,

Impenetrability