以外(いがい)Except・besides, Other than, With the exception of

Both forms can express the idea of 'other than', but their nuance and usage differ slightly. いがい emphasizes exceptions, like 'except for' or 'other than,' and attaches directly after nouns, e.g. バナナ以外の果物 means 'fruits other than bananas.' In contrast, ほかに highlights the presence of alternatives, takes の when linking to nouns, e.g. バナナの他に 'other than bananas', and can also start a sentence or phrase.

いがい and を除いて both express exclusion, similar to 'other than' or 'with the exception of' in English. Their meanings are very close and often interchangeable. The main difference is that を除いて is more formal and mainly used in writing, while いがい appears in both casual speech and writing. 土日以外毎日働いています and 土日を除いて毎日働いています both mean 'I work every day except Saturday and Sunday.'.

はともかく carries the nuance of setting something aside to focus on the rest. For example, 田中さんはともかく、みんな来ると思う means 'Setting Tanaka aside, I think everyone will come.'. In contrast, いがい emphasizes exclusion, 田中さん以外はみんな来ると思う means 'I think everyone but Tanaka will come.' So, はともかく avoids commenting on Tanaka, while いがい explicitly excludes him.

Both forms express exclusion, but with key differences. いがい (often written in kanji as 以外) attaches directly to nouns, e.g. サッカー以外 'other than soccer'. It's common in both speech and writing. In contrast, をおいてほかに〜ない is much more formal and academic. It's also used almost exclusively to positively highlight something, while いがい carries no such nuance.