So far as one can is a phrase used to express the extent of something that is known or possible. It is often used when discussing something that is uncertain or speculative. There are several synonyms for this phrase which include 'to the best of one's knowledge', 'as far as possible' and 'to the extent of one's ability'. The synonyms convey the same meaning as 'so far as one can' and can be used interchangeably in a sentence. The use of synonyms offers variety in language use and provides alternative expressions for conveying similar ideas.