In theory means on paper, according to the plan or calculation: in theory, all six shelves should fit. Most of the time it sets up a but: in theory it's simple, but in practice... No science is needed: a plan, a manual or a quick estimate is enough.
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In theory, + expected or possible situation / could or should + in theory + verb
- In theory, all six shelves should fit along this wall.
- One person could, in theory, run the desk and answer the phone.
- The battery should last all weekend in theory, but we have not tested it outdoors.
What changed
First versionIn the theory, the boxes should fit in one van.
RevisionIn theory, the boxes should fit in one van.
Theory is an ordinary countable noun, so the theory seems right. But when it means on paper, the phrase has no article: in theory. The is needed only for a specific named theory: in the theory of evolution.
In principle often means agreement in general: we agree in principle. In theory is about calculation and expectation: in theory, it should work. The pair in theory and in practice compares plan and reality, while in principle is agreement without the details.
Your turn
The plan should work on paper: It is possible in ___.
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theory — When it means on paper, no article is used: in theory. The theory needs a specific theory to be named.
Describe a plan that will only work under one condition, and say what still needs checking. Use in theory.
In theory, the desk will fit through the doorway, but we still need to measure the handles.
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