My colleague and I were talking and he said "it should have came down", which to me, does not sound correct. Which sentence is correct?
I also have a question about 'took' and 'taken'. With the same individual, he said "he could have took the cookie" to which I corrected him and said that, yes, you can say that and the meaning will come across and will be understandable, but "he could have taken the cookie" is correct English. In retrospect, after much debate, I am now doubting myself.
By my knowledge of the English language, 'took' and 'taken' are not interchangeable if you are utilising the English language correctly.
Best Answer
The constructions you are quoting are of the should have + past participle type.
Here, the verb to come is used in its preterite ("simple past") form, which is wrong.
Here, the verb to come assumes its past participle form, as it should after should have.
The same is true with could have took (wrong) and could have taken (right). In short, you were right in both cases.
Why? Because the modal verb should and the verb have play auxiliary roles (they are "auxiliary verbs"). The carry some information, and the verb coming after them is left to carry the rest.
The auxiliary verb have already tells us that the action is in the past, so we don't need the simple past form of the verb to come. We need to attach a "weaker" verb after the have, a verb that merely carries the information about the kind of the action (to come) and not about the time of the action. Otherwise, we would have a "much of a muchness" situation.
The Past Participle is such "weaker form": a non-finite verb.