Across vs. Through: What's the Difference?

• Movement on a Physical Surface: This is the most common usage. Across describes movement from one side of a surface to the opposing side. The surface can be a flat plane, water, or even a vertical surface if the movement is perceived as spanning its width.
• She ran across the field to catch the ball. (Movement on an open, flat area.)
• We sailed across the Atlantic Ocean in three weeks. (Movement on the surface of water from one side to another.)
• A spider crawled across the wall. (Movement on a vertical surface, spanning its width.)

• Spanning or Extending: Across can also indicate that something extends or lies from one side to another, without necessarily implying movement of the subject itself. Here, it functions more as a preposition of place describing arrangement.
• A long scar ran across his face. (The scar extends from one side of his face to the other.)
• They built a bridge across the gorge. (The bridge spans the width of the gorge.)
• The news spread rapidly across the entire continent. (The news extended its reach over the area.)

• On the Opposite Side/Location: In some contexts, across denotes a static position on the other side of something, functioning similarly to opposite or on the other side of. This is common when giving directions or describing relative locations.
• The new bookstore is just across the street from the bank. (Its location is on the opposing side of the street.)
• We could see the mountains across the valley. (The mountains were located on the other side of the valley from our viewpoint.)

• Metaphorical or Abstract Spanning: Across can be used to describe the bridging of abstract boundaries, such as time, cultures, or disciplines. It implies a connection or shared experience over a particular domain.
• Her music appeals to people across all generations. (It connects with different age groups, spanning them.)
• This research has implications across various scientific fields. (Its relevance extends over different areas of science.)

• Movement within an Enclosed Space: This is the core meaning. The space could be an architectural structure, a natural formation, or even a dense collection of objects or people. The movement implies entering at one point and exiting at another, being fully enveloped during the process.
• The train sped through the long tunnel. (Movement inside a confined, artificial structure.)
• We hiked through the dense jungle for hours. (Movement amidst and surrounded by trees and vegetation.)
• The children pushed their way through the crowded market. (Movement amidst a mass of people, being surrounded.)

• Movement within a Medium or Substance: When you move within a fluid or diffuse substance, through is the appropriate choice. This emphasizes the immersive nature of the movement.
• A submarine travels silently through the water. (Movement submerged within a liquid medium.)
• Birds fly gracefully through the air. (Movement within an atmospheric medium.)
• We drove cautiously through the thick fog. (Movement immersed in a gaseous medium.)

• Penetration or Passage via an Opening/Barrier: Through indicates that something passes into and out of another object or material, or moves via a hole, gap, or transparent barrier. It often implies a point of entry and exit.
• The bullet went straight through the wall. (Penetration of a solid object.)
• Light filtered through the stained-glass window. (Light passing via a transparent barrier.)
• He could barely see through the tiny keyhole. (Vision passing via a small opening.)

• Process, Duration, or Completion: Through is frequently used metaphorically to describe the enduring of a period of time, the completion of a process, or the experience of a difficult situation. It implies moving from the beginning to the end of something non-physical.
• We worked through the entire weekend to finish the project. (Enduring a period of time until its completion.)
• She's trying to get through her final exams. (Navigating and completing a challenging process.)
• After a long discussion, they finally talked through their differences. (Completing a process of communication to resolve issues.)

• Means or Medium (Instrumental Use): Less commonly, through can indicate the means by which something is achieved or communicated, acting as an intermediary.
• They communicate through an interpreter. (The interpreter is the medium of communication.)
• We learned about history through old letters. (The letters are the means of acquiring knowledge.)

You typically walk or pass through a doorway or through a door because it's an opening you go inside of to transition between spaces. You look through a window because your gaze passes via the glass, which acts as a medium. If you're talking about the window frame itself, you might say The cat jumped across the windowsill (on the surface).

Yes, absolutely. When you swim across a river or drive across a bridge over a river, the focus is on moving from one bank or side to the other, treating the river (or bridge) as a surface or a span to be covered. However, a submarine moves through the water because it is immersed within the volume of the liquid. Similarly, fish swim through the water.

You usually think through a problem or talk through an idea, implying a process of internal exploration and comprehensive examination from beginning to end. You can get an idea across to someone, meaning to make it understood, effectively spanning the communication gap. You might also spread an idea across a community, indicating its propagation over a broad group.

Both are very common phrasal verbs, but with distinct meanings directly related to the core prepositions. Go across means to move from one side to the other of a surface (go across the road). Go through means to pass into and out of an enclosed space, experience a process, or search something thoroughly (go through the tunnel, go through a difficult period, go through your old photos). The choice depends entirely on the context and the meaning you intend.

Not always. While there's overlap, over often implies going above something (e.g., jump over the fence). Across implies going from one side to the other on the same level or on a surface (e.g., walk across the field). However, walk over the bridge and walk across the bridge are often interchangeable because a bridge is a surface that also allows you to go "over" an obstacle (like a river or gorge). The choice can sometimes be stylistic or emphasize slightly different aspects of the movement (spanning vs. elevated passage).

For sound, you typically use across when it travels over an open space: The music carried clearly across the lake. For light, you generally use through when it passes via a medium or an opening: Sunlight streamed through the window. or The laser beam cut through the air.

Yes, definitely. One of the powerful metaphorical uses of through is to denote reaching the end of a process, a task, or a difficult period. For example, I made it through the hardest part of the project means you have completed or survived that stage. Once you get through this book, you'll understand implies finishing the reading.

Imagine a piece of paper: you draw a line across it. Now imagine a hollow tube: you push a string through it. If you can move on top of or over something to get from side to side, across is likely correct. If you have to go inside, between, or amidst something to get from one end to the other, through is probably the better choice. It's about whether you're skirting the boundary or immersing yourself within.