1. Tense and aspect are often not easily separated, and languages may make aspectual distinctions hand in hand with tense restrictions.

2. Languages may conflate tense and aspect into one form. In English, the sentence "I built houses" has a habitual (imperfective) aspectuality, while "I built a house" has a perfective aspectuality.

3. The properties of arguments in the clause can affect the temporal or aspectual interpretation of the sentence. 

4. Tense is not always a verbal category, and it can be marked on nouns as well. In Guarani, nouns can be marked for tense, as in "h-6ga-kwé" (his former house) and "h-emiap6-ra" (his future work).

5. Nouns can take over the verb's job and attract the tense marking for the whole clause. In Siriondé, nouns can attract the tense marking for the whole clause, as in "Esi-ke 6so fia ii-ra" (The woman went near the water) and "Jyvkv-ke uke-rv" (The tiger slept).

1. Tense Systems:

 Languages divide time into different segments for grammatical purposes.

 Common systems include past, present, and future, but languages can have different divisions, such as non-past/future.

 Example: Dyirbal distinguishes future and non-future tenses.

2. Inflectional Future Tense:

 Some languages mark future tense through inflectional endings.

 Example: Lithuanian has an inflectional future tense suffix "-siu."

3. Non-Present Tense:

 A rare distinction is present vs. non-present, where past and future are coded by a single form.

 Example: Hindi has a lexical term "kal" that can refer to both yesterday and tomorrow.

4. Metrical Tense:

 Some languages use distinct grammatical forms to measure temporal distance from the present.

 Example: Yagua has five different past tenses that indicate varying degrees of remoteness.

5. Past Tense:

 Most languages have a past tense, but some do not.

 Example: Yagua has no grammatical past tense.

6. Aspectual Distinctions:

 Many languages distinguish between perfective (completed) and imperfective (ongoing) aspects.

 Example: In English, the distinction is often marked lexically (e.g., "break" vs. "be breaking").

 Languages can also have different ways of expressing aspectual types, such as through verb hierarchy.

Main Theses:

 Languages exhibit diverse approaches to grammaticalizing time and aspect.

 Aspect can be independent of tense, as in Slavic languages.

 When both tense and aspect are marked grammatically, aspect tends to precede tense.

 This order reflects the greater relevance and scope of aspect to verb meaning.

Examples:

 Slavic languages: Russian verbs are categorized as perfective or imperfective, independent of tense.

 Turkish: Aspect morphemes (e.g., "-iyor-") appear closer to the verb stem than tense morphemes (e.g., "-du-").

 Bybee's cross-linguistic study: Aspect morphemes consistently appear closer to the stem than tense morphemes, suggesting their higher relevance to verb meaning.

1. "Tenseless" languages exist: Some languages do not have grammaticalized tense but rely on temporal adverbs or other means to imply time reference.

 Example: Burmese relies on mood markers and time adverbials.

2. Close association of aspect and time reference: In languages without tense, perfective aspect is often associated with past time reference, while imperfective aspect is associated with present time reference.

 Example: Mandarin Chinese uses the perfective aspect for past events and the imperfective aspect for ongoing events.

3. Diverse ways to express time: Different languages use a wide range of linguistic devices to express temporal relationships, including tense, aspect, adverbs, and other grammatical markers.

 Example: English has a complex system of tense markers, while Japanese uses a combination of tense markers and particles to indicate time reference.

4. Cultural and cognitive factors: The specific ways in which a language expresses time can be influenced by cultural and cognitive factors.

 Example: Some languages have a more finely grained system of tense markers than others, reflecting the importance of temporal precision in their culture.