Is the word "actually" redundant in the context?

Question

Some psychologists believe that we can explain every decision or choice that an individual makes by referring to some earlier conditioning that the individual has undergone, so that, although the individual might feel free, his or her action is in fact entirely determined by what has happened in the past, and by genetically transmitted predispositions. We cannot know for certain that this isn’t actually the case.

Philosophy: The basics

I don't know the use of "actually" in the context above. Is it redundant? Is there any difference between "this isn’t actually the case" and "this isn’t the case"?

I tried to understand the bold sentence like this: We cannot know for certain whether this is actually the case or not. Is my understanding correct?

Many thanks

Answer 1

Semantically might be redundant (it does not change the meaning), yet overall it's not redundant: it lends an emphasis otherwise not achieved.

As per dictionary.com:

Actually
A parenthetic filler used to add a slight emphasis

I believe in this sentence it emphasizes that the author/speaker indeed, really does not know whether this is the case or not; additionally, they distance themselves from being an authority in determining it.

Also, there is an additional thing at play here:

Your quote, actually, is just two sentences. The first, very long, complex one is the non-bold, while the second is the very short bold one.

I believe when following this long and complex sentence, the short bold one has a chance to miss its impact — simply due to how it's off-pattern compared to the rhythm of the rest of the speech. Injecting actually into this short, quick sentence lends it extra volume and a variety of pattern, thus makes it more remarkable, more prominent. This should help the reader to pick up the meaning of the entire paragraph with less effort.