Final answer:
In English, the 'tch' spelling of the /ch/ sound is usually used after a stressed short vowel or in a VCC string, while the 'ch' spelling is used in other cases.
Step-by-step explanation:
In the English language, the 'tch' spelling of the /ch/ sound is typically used in the circumstance when it comes after a stressed short vowel or in a VCC string.
For example, in words like 'itch', 'watch', and 'patch', the sound [ch] is spelled with a 'tch'.
However, in most other cases, the 'ch' spelling is used, such as in words like 'chalk', 'research', and 'teacher'.