Is it true that the tones of some of the most common words are glossed over in regular speech/turn into neutral tone?

Question

Examples include: 是、去、在、要、就、但、没有、如果

Not sure how to back up this question, except to mention that I've received feedback from natives that I tend to overdo these words' pronunciations (especially 是）. I've also seen 是 labelled as shi0 instead of shi4 in a few textbooks. Also, when I listen to native speech, I am under the impression that a handful of words in a sentence are naturally (perhaps automatically) glossed over/sped up in order to stress the more important words in a sentence (and, for natives, this I imagine is done for the sake of convenience too).

From these observations, I've surmised that the tones of common words in daily speech are usually glided over more rapidly than other words that are not as common (particularly in situations where it is clear which word is intended e.g. 我是学生 cannot be interpreted as *我时学生 etc).

Is there any credit to this hypothesis? Is it okay to do the same as a learner i.e. to glide over some of the more commonly spoken words in a regular conversation?

Similar posts: What difference(s) does it make to use the citation tone instead of the neutral tone, for the tail character in these words?

words where it is important to distinguish between the neutral tone and the citation tone especially @L Parker's point number 5 on quasi-neutral tones

Answer 1

1. I discussed quasi-neutral tones in the fifth point of my answer to another question here. Salient points include:

   • Usually, a stress is placed elsewhere in the sentence. Such words (edit: usually frequent words / function words, i.e. 虛詞) are therefore weakened in their presence. See the three examples in my orginal answer for more details.
   • The tone sandhi is facultative (i.e. the citation tone and quasi-neutral tone coexist), not obligate.

2. They are not glided over when, e.g.:

   • There is pragmatical reason to place stress on them. You emphasise 是 in 我是學生 when e.g., someone is doubting your identity as a student. Interestingly, 學生 may become relatively toneless in the presence of a stressed 是, especially in rapid speech.

   • There is contextual reason to place stress on them, e.g., when you are delivering a speech (especially the 朗誦 kind that values intonation, more so than 演講). Otherwise, in oral exams, if you are expected to be conversational, gliding over is permissible, even more natural.