A speaker is actually starting a video "right over there", why does he use the subjunctive mood?

Question

At the beginning of a video, the speaker says

In the last video, I hinted that things were about to get wacky. And they are.

So if we start where we left off in the last video, we started right over here, looking at the distance to the nearest star.

I re-paragraphed the starter as the one above. I guess the speaker is trying to use the subjunctive mood

if we started …

However, he is actually starting the tutorial "right over there", why does he use the subjunctive mood?

The video where the question comes from is named "Scale of the galaxy" and the previous video is named "Scale of distance to closest stars" where at the end of that video the speaker explains the distance to the nearest star.

Answer 1

This kind of "introductory if" is a pretty common idiom, particularly in academic English, when presenting things to an audience. (Actually, I believe it's a cross-linguistic phenomenon — I've encountered its equivalent in several other European languages too.) You'll often hear presenters say things like:

"Now, if we look more closely at this section of the diagram, we'll see that…"

or:

"If we let X take a negative value, however, what happens is that…"

This is also reasonably common in academic writing, although perhaps not as common as in speech. I would say that the point of the "if" in such sentences is two-fold:

1. Semantically, it often serves to introduce a condition (such as X < 0 in the second example above) from which the following conclusions or observations then follow. However, especially is speech, this formal logical structure won't always hold — the speaker might instead decide to segue into something that is only tangentially related to the specific assumption or action that they invited the audience to consider with the "if".

   In your example quote, in particular, the speaker is clearly changing the mood and the focus mid-sentence, in a way that's not strictly grammatical but often common in speech. It basically sounds like they're originally planning to say something like:

   "So if we start where we left off in the last video, we can see that…"

   but instead they decide to insert a brief summary of where they, if fact, left off in the last video, something like this:

   "So if we start where we left off in the last video — right over here, looking at the distance to the nearest star — we can see that…"

   but then they just keep extending the summary of where they left off more and more, into multiple sentences, until neither they nor the audience likely even remember that there was an interrupted sentence that should be technically be continued at some point. Indeed, if the speaker did choose to finish their original conditional sentence at some point, maybe a minute or two later in the video, that would be a lot more confusing than just leaving the sentence unfinished.

   And that's fine; that's how spoken language works. We can only keep so much grammar stored up in our short-term memory while also trying to pay attention to other, more important things, like the substance of what's being presented. Sometimes it's better to just leave unfinished sentences unfinished.

2. In addition to its formal logical role, the "if" also serves as a politeness marker: it invites the listener or reader to follow along with what the presenter is doing, but doesn't come across as ordering them to do so. The examples I gave above would come across a lot more blunt, and potentially rude and jarring, if presented without the conditional, like:

   "Now we will look closely at this section of the diagram, and we will see that…"

   or even:

   "Now, look closely at this section of the diagram, and you will see that…"

   Now, this kind of "direct" presentation style, where the speaker directly addresses the reader in the imperative mood, can in fact sometimes work quite well, and some presenters like it. But many don't, as it does require a certain extra level of confidence and assertiveness to pull off well. The conditional style is a lot less assertive — basically what the presenter is implying with the "if" is that "I know I can't force you to pay attention to this, but please humor me and follow along even if you think I'm presenting this stuff in a different way than you'd prefer."

Answer 2

It is spoken English, and it seems that the speaker changed their mind about how they would express something:

They begin

If we start where we left off in the last video ...

probably intending to continue ... I will be able to explain about the stars.

But then changed their mind and decided to review the start of the last video (So they won't start where they left off, first they will review...)

It's an error that would be corrected in a written document, but is perfectly natural to just to leave it when speaking.

Answer 3

It sounds to me as if the speaker went off on a series of digressions and lost his train of thought. So the sentence was never completed.

Let’s take a similar sentence that might be like what he started out intending to say. I’ll add a few extra words for clarity.

So if we [were to] start where we left off in the last video, [because] we [previously] started right over here, [...] we would be looking at this.

In this case, the main “if” clause is in the future subjunctive. declaring his intent to do something in the immediate future. It’s a pretty formal way to say this, compared to, “Let’s start where we left off,“ or “We’ll start where we left off.” The second clause, with “started,” is simple past tense, stating what happened last time.

Then I made up a third clause that completes the sentence in a way that makes grammatical sense. The prof, speaking extemporaneously, doesn’t say anything like that. After, “right over here,” he breaks off into a series of digressions (“and just as a reminder, ...”) for more than a minute, and when he’s done, he never comes back and ends his first sentence. Either he’s lost his original train of thought, or he decides it would be better to move on.

Another way to parse this statement is that he starts out introducing the video one way, then changed his mind and did it another way. So, perhaps, he’s first saying, “So if we start where we left off—” but he rephrases that as, “We previously started right over here, and just as a reminder [....]” Then the first clause would be a sentence fragment. If he’d said, “We’ll start where we left off,” or “Let’s pick up where we left off,” either would have been a complete sentence and there would be no confusion. A false start like that would usually be edited out of a video, but you unfortunately can’t do that in a live lecture.

Answer 4

It's a tutorial video. Doesn't mean that he's trying to teach English :) So he/she might slack off a bit with the grammar. The speaker is teaching about stars if I understand correctly.

Your point is correct. He shouldn't use the subjunctive mood.