一日たりとも勉学を怠ってはいけない。
- You must not neglect your studies even for a single day.

一日たりとも勉学を怠ってはいけない。 meaning: You must not neglect your studies even for a single day.

The sentence follows a classic Japanese structure, which involves the subject (often implied), followed by a topic marker (sometimes omitted), and then the object and verb. The sentence, in essence, is a negative imperative, issuing a strong prohibition. ⚫︎ Subject (implied): "You" (or "one," implying a general rule) ⚫︎ Object: 勉学 (studies) ⚫︎ Verb: 怠ってはいけない (must not neglect) ⚫︎ Adverbial phrase: 一日たりとも (even for a single day) modifies the verb, indicating the duration or extent of the prohibition.

たりとも is a fixed expression used to emphasize the negation that follows, often intensifying the degree of the statement. It's often used with negative verbs. ⚫︎ Its primary function is to mean "even," "not even," or "for as much as." ⚫︎ It usually follows a unit of time, quantity, or degree, such as 一日 (one day), 少し (a little), etc. ⚫︎ It emphasizes that even a minimal amount or degree is prohibited or undesirable. ⚫︎ Example: 彼はお金が一日たりともない。 (He doesn't have any money, not even for a day.)

The particle も following たり in this expression, intensifies the meaning. ⚫︎ The も particle adds emphasis, suggesting "even," "also," or "as much as" to the preceding word or phrase. ⚫︎ The phrase 怠ってはいけない uses the negative form of the verb 怠る (to neglect, to be negligent). ⚫︎ 〜てはいけない is a form of prohibition, meaning "must not" or "you must not." It is a negative imperative. ⚫︎ Combining たりとも with the negative verb form creates a strong, emphatic prohibition. For example, 少しも行かない means "won't go at all."

Understanding the verb conjugation is essential for comprehending the sentence's meaning. ⚫︎ The base verb is 怠る (to neglect, to be negligent). ⚫︎ The stem of 怠る is 怠り. ⚫︎ The te-form of 怠る is 怠って. ⚫︎ The negative imperative form: 〜てはいけない is a crucial structure to master. It indicates a strong prohibition. It means "must not" or "should not." ⚫︎怠ってはいけない is formed by attaching はいけない to the 怠る te-form, showing an emphatic prohibition.

The auxiliary verb phrase 〜てはいけない is crucial for the sentence's overall meaning. ⚫︎ 〜てはいけない combines the te-form of a verb with the negative auxiliary verb はいけない. ⚫︎ はいけない expresses "must not," "should not," or "it is not permissible to." It implies a strong prohibition. ⚫︎ This construction is used to issue commands, give advice, or express a sense of necessity about what *not* to do. ⚫︎ In this sentence, 怠ってはいけない stresses a strong prohibition against neglecting studies, making the message very clear and emphatic.