✨ Basic Meaning
🎯 Primary Function
📋 Grammar Structure
🎭 Usage Contexts
Can be used in moderately formal contexts, but it’s more common in general conversation and less formal writing. For highly formal or academic writing, more objective expressions of cause might be preferred.
Very commonly used in informal conversations among friends, family, and colleagues.
Appears in various forms of written language, including casual essays, blogs, emails, and fiction, reflecting the speaker’s speculation.
Highly frequent in spoken Japanese, as it naturally conveys a speaker’s thought process and slight hesitation about a cause.
💡 Common Applications
📌 Important Points
⚠️ Common Mistakes
🏛️ Cultural Context
🔍 Subtle Differences
📝 Conjugation Notes
Connects to verbs, i-adjectives, and na-adjectives (plain form) and nouns (with の). For na-adjectives, it can be stem + な + せいか or stem + である + せいか, with な being more common in spoken Japanese.
🔊 Pronunciation Tips
The ‘sei’ (せい) part is pronounced like ‘say’. The ‘ka’ (か) has a slight upward intonation if it’s genuinely questioning, but often it’s just part of the grammar pattern and doesn’t carry a strong questioning tone like an interrogative particle.
🧠 Memory Tips
Think of 「せい」 as ‘reason’ or ‘fault’ and 「か」 as ‘perhaps’ or ‘I wonder if’. So, ‘reason, perhaps?’ is a good mnemonic for ‘uncertain cause’.

I’m a software engineer based in Japan, with experience in developing web and mobile applications. I’m passionate about technology, especially in DevOps, AI, and app development using platforms like AWS, Flutter, and Node.js. My goal is to build a website that shares knowledge about the Japanese language and IT, helping everyone learn and grow more easily in the digital era.