Which is proper in this sentence: ‘assurance’ or ‘assurances’

Then suddenly, despite all their ______ (assurance/ assurances), they broke the agreement and signed a deal with a rival company.

I’m not sure which form of the word ‘assurance’ should be taken in this sentence. I think the word assurance itself means ‘promise’ here, but not ‘ confidence’ , and according to the dictionary it’s a countable noun. But our teacher provides us with the answer ‘assurance’ the single one. Is the answer wrong?

Solution 1:

The same word can have different meanings. It is often the case that with one of the meanings the word is countable, and with the other, not.

If you can put "a" or "an" in front of the noun for the meaning in question, it is always safe to use the plural with all

We can give someone "an assurance", that is, a guarantee or promise, so:

... despite all their assurances ^{(i.e. promises)} , they reneged

... The lawyers filed many pleadings ^{(i.e. legal motions, submissions)} seeking damages, but despite all their pleadings, their client did not receive a penny.

When an article is not used (with the particular meaning in question) use the singular:

... despite all her assurance ^{(i.e. self-confidence)} she felt ill-at-ease in front of a large crowd

... despite all their pleading ^{(i.e. imploring, begging)} they were sent to bed with no TV