Insofar vs. In So Far
Both “insofar as” and the open form “in so far as” are established ways to express “to the extent that.” The closed form is a dictionary headword, while references also record the open construction, so house style and consistency can determine the choice.
“Insofar as” and “in so far as” are both established; use the form your style requires and keep it consistent.
Key details
Choose the right form
| Form | Status | Editing choice |
|---|---|---|
| insofar as | Established closed form | A compact default when your style permits it. |
| in so far as | Established open form | Also acceptable; retain it when required by house style or source text. |
| Mixed forms within one document | Avoid without reason | Consistency is usually more useful than treating one established form as universally wrong. |
Quick tests
Consistency test
Does your house style specify one of the established forms?
If yes: Follow that form consistently.
If no: Choose one established form and keep it consistent within the document.
Caveat: Both forms are documented; this is not a meaning contrast.
Examples
Insofar as the evidence supports the claim, we can proceed.
The closed form is established.
In so far as the evidence supports the claim, we can proceed.
The open form is also established; a house style may determine the choice.
Further guidance
Core difference
The closed and open forms can express the same “to the extent that” relationship, especially in the construction “insofar/in so far as”.
Usage Boundary
Do not mark the open form automatically wrong merely because the closed headword is common; use a consistent editorial form.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- insofar — Collins English Dictionary (opens in a new tab)Collins English Dictionary · Established closed form insofar and its “to such an extent” meaning
- in so far as — Collins English Dictionary (opens in a new tab)Collins English Dictionary · Established open form in so far as