せいか details
write + perhaps because
kaku sei ka
perhaps because; maybe it's because — the cause offered only as a guess
寝不足のせいか、今日は全然集中できないんだよね。
nebusoku no sei ka, kyou wa zenzen shuuchuu dekinai n da yo ne.
Maybe it's the lack of sleep, but I just can't concentrate at all today. casual
雨が続いたせいか、今年のトマトは小さい。
ame ga tsuzuita sei ka, kotoshi no tomato wa chiisai.
Perhaps because of the long spell of rain, this year's tomatoes are small. neutral
- dictionary form
- i-adjective
- na-adjective
- noun
Examples
perhaps because — the speaker names a likely cause for something they have actually noticed, without committing to it
寝不足のせいか、今日は全然集中できないんだよね。
nebusoku no sei ka, kyou wa zenzen shuuchuu dekinai n da yo ne.
Maybe it's the lack of sleep, but I just can't concentrate at all today. casual
雨が続いたせいか、今年のトマトは小さい。
ame ga tsuzuita sei ka, kotoshi no tomato wa chiisai.
Perhaps because of the long spell of rain, this year's tomatoes are small. neutral
気のせいか、さっきより風が強くなった気がする。
ki no sei ka, sakki yori kaze ga tsuyoku natta ki ga suru.
Maybe I'm imagining it, but the wind feels stronger than it did. neutral
連休明けのせいか、本日はお問い合わせが少なくなっております。
renkyuu ake no sei ka, honjitsu wa o toiawase ga sukunaku natte orimasu.
Perhaps because the holidays have just ended, enquiries are down today. formal
Formation
{V}せいかattaches to dictionary formplain clause + せいかattaches to plain clause{I}せいかattaches to i-adjective{NA-stem}なせいかattaches to na-adjective{N}のせいかattaches to noun
Notes
Sentence-final せいだろうか keeps the guess but drops the following clause.
Related patterns
Similar
せいで asserts the causal link outright and hands out blame for it (電車のせいで遅刻した); せいか floats the same cause as no more than the speaker's guess, so the sentence survives the guess being wrong — and because the attribution is hedged, せいか takes results that are merely noticeable (年のせいか目が疲れる), where せいで would read as an accusation.
かもしれない hedges the CLAIM (雨が降るかもしれない leaves the rain itself open); せいか hedges only the causal LINK and asserts the result flatly — 疲れているせいか字が汚い states that the writing is messy and guesses only at why.