だTo be, Is

だ conveys a casual, informal, or blunt tone, except when required by certain grammatical patterns. In contrast, でございます is a highly polite form, primarily used in business settings or when addressing someone of higher social status such as a boss or customer.

だ and です both function like the English 'is.' The main difference is politeness: だ is casual and used in plain speech, while です is polite. だ can't be used after い-adjectives, but です can, acting as a general politeness marker. You may still see だ in set expressions like ～だと思います, even in polite sentences.

The main difference between だ and である is formality. だ is casual and common in conversation, while である is more formal and mainly used in writing. Both だ and である follow nouns or noun phrases, but である has a more literary tone. である slight differs from the verb ある (to exist) in that である is a fixed connector.

だ follows nouns and な-adjectives, with a meaning similar to the English 'is.' For instance, これはペンだ translates to 'This is a pen.' On the other hand, じゃない (a contraction of ではない) is used to create the negative of such expressions. For example, これはペンじゃない translates to 'This isn't a pen.'

がある indicates the existence or possession of something. For example, ペンがある means 'There is a pen (on the table, etc.)' or 'I have a pen.' On the other hand, だ expresses assertion or determination similar to 'is/are' in English. In contrast to the がある example, ペンだ would mean 'It (=the thing we are looking at) is a pen.'

だった・でした and だ are all used to assert or identify something. The difference among them is in formality and tense. だ is casual and present tense (similar to the English 'is'/'am'), while だった・でした is past tense ('was'), with だった being casual (the past tense of だ) and でした being polite (the past tense of です).

よ is a common sentence-ending particle used to add emphasis, often indicating the speaker is sharing new information (e.g., 面白いよ = 'It's interesting, I'm telling you!'). だ is a grammatical form expressing assertion, similar to 'is' or 'am.' These two are often combined, especially in casual or masculine speech (元気だよ = 'I'm feeling good!'). In softer or more feminine speech, the だ is frequently omitted (e.g., 元気よ).