Generally, you should spell out numbers one through nine. This includes ordinal numbers like "first," "second," "third," and "fourth."
Exceptions:
* Technical writing: In technical writing, numbers are often written as numerals, regardless of their size. This helps to prevent ambiguity.
* Style guides: Some style guides, like the Chicago Manual of Style, recommend using numerals for all numbers above nine.
* Numbers with units: Always use numerals when a number is followed by a unit of measurement (e.g., 4 feet, 25 seconds).
* Dates: Always use numerals for dates (e.g., June 14, 2023).
Examples:
* Correct: "The fourth chapter of the book discusses..."
* Correct: "The book has 24 chapters." (Technical writing, Chicago Manual of Style)
* Correct: "They waited for 4 hours." (Number with unit)
* Correct: "The meeting is on March 15th." (Date)
In conclusion: While it's generally recommended to spell out "fourth," there are exceptions depending on context and style guidelines. Always refer to the specific style guide you're using for guidance.