が details
write + but
kaku ga
but; and — contrast or soft preamble
練習は重ねたが、決勝では勝てなかった。
renshuu wa kasaneta ga, kesshou de wa katenakatta.
We put in the practice, but we couldn't win the final. neutral
すみませんが、窓を閉めていただけますか。
sumimasen ga, mado o shimete itadakemasu ka.
Excuse me, but could you close the window? neutral
Examples
but — two clauses in contrast, in polite speech and writing
練習は重ねたが、決勝では勝てなかった。
renshuu wa kasaneta ga, kesshou de wa katenakatta.
We put in the practice, but we couldn't win the final. neutral
検討いたしましたが、今回は見送らせていただきます。
kentou itashimashita ga, konkai wa miokurasete itadakimasu.
We have given it consideration, but we will pass on this occasion. formal
soft preamble — が hands over context with no real contrast, cushioning a request or introduction
すみませんが、窓を閉めていただけますか。
sumimasen ga, mado o shimete itadakemasu ka.
Excuse me, but could you close the window? neutral
もしもし、田中と申しますが、鈴木さんはいらっしゃいますか。
moshi moshi, tanaka to moushimasu ga, suzuki-san wa irasshaimasu ka.
Hello, this is Tanaka calling — is Suzuki-san there? formal
Formation
{V}がattaches to dictionary formplain clause + がattaches to plain clausei-adj + が (高いが)attaches to i-adjectivena-adj + だがattaches to na-adjective{N}だがattaches to noun
Notes
Related patterns
Similar
The same connective "but" split by register — けど is the spoken default and drifts casual, が belongs to polite speech and writing; in a business mail mid-sentence が is the safe pick, in chat けど is.