When does てきた take place? Is it representing an ongoing change or not?

Question

Quick Notice: For many months now I've been struggling with てくる and it's exact meaning when dealing with time flow and indication of change. I do however, understand, when it is used with movement or some action that is coming towards the speaker (I think). I have looked at numerous resources including other posts on here, youtube videos and grammar guides alike.

Anyhow, here I have listed out example sentences with the English translations that were provided:

1. 涼しくなってきた
   It's getting cooler.
   It's starting to get cooler.

Obviously here the big difference between the translations is that the second translation indicates that the gradual change from hot to cool has just started whereas the first translation doesn't give a time frame for the starting point at all. The first translation sounds like it has been getting cooler for sometime perhaps. I suppose I just don't understand which interpretation is correct or more accurate, or if they are both accurate (somehow)? I also don't understand why both English translations are in the present perfect tense and why this change didn't occur in the past?

2. お城が見えてきた。
   The castle is coming into view.
   

Again with this translation it sounds like maybe the castle has been coming into view for a while. Nothing has indicated that the change has just started. Could it also be interpreted as, "The castle started coming in to view."? Also, again, why is the gradual change here, interpreted to be in an ongoing state and not in the past like the next examples?

3. 日本語が話せるようになってきた。
   I have gotten good at speaking Japanese.

4. 日本での生活に慣れてきた。
   I have gotten used to life in Japan.

5. 日本語学習者の数が増えてきた。
   The number of people studying Japanese has increased.

In these translations (3-5), the gradual change is indicated to be sometime in the past and it doesn't indicate whether the gradual change is on going or not. In comparison, the first two translations indicate that the gradual change is still ongoing.

How can I tell when てきた is indicating a change from the past 'till the present vs change that is just starting like the first two examples? Also how can I tell if it's something that is still ongoing or if the change is in the past? This has been a total mess in my head for so long now, if anyone could provide me with insight that would be great, thanks!

Answer 1

First of all, [V て-form]-きた is a somewhat subjective expression in the sense that whatever has come has come to the speaker. For example, when you say 涼しくなってきた, you are experiencing the coolness yourself. The sentence doesn’t say when the change started to happen, but it implies you, as the speaker, have just noticed it and perceive it as ongoing. If you perceive it as a one-time change in the past, you would say 涼しくなった.

It’s hard to pinpoint the beginning of the change in the case of 涼しくなってきた. It could be days or even weeks earlier. This lack of a clear beginning suggests the change is gradual. The change in, say, 雨が降ってきた, on the other hand, is instantaneous and more obvious, and therefore, you are expected to notice it soon after it happens. In such a case, the construct is understood as indicating that something has just begun to change. You don’t need to get wet, but you still perceive the rain as your own experience. If you are talking about rain in some remote place as an objective observer, you would say 雨が降り始めた or 雨が降り出した, instead.

The change in お城が見えてきた could be either gradual or instantaneous. The most likely scenario would be that you are moving towards the castle, and at one point it comes into your view from behind whatever was blocking it. It’s hard to not notice something when it has just come into your view like that. If you don’t notice it, it’s still out of your view, after all. Then, the sentence is understood as indicating something has just begun to change just like 雨が降ってきた. However, it’s also possible that your view was obscured by clouds, mist, or some problem with your eyes, and as it gets cleared up, the castle has become visible. This would be a gradual change. This distinction is a relative one. You might even say 涼しくなってきた in response to a sudden drop in the temperature in an air-conditioned room, for that matter. What’s important is you have just come to realization and you are experiencing it.

Your last three sentences also imply the change is ongoing as the speaker perceives or observes it. Otherwise, you would use simple た-forms. If this distinction is hard to express in English, it could be due to the subjective nature of the construct. The last sentence might not sound as subjective as the others, but you are still speaking from within the environment where the change is going on.

Answer 2

Your confusion comes from the fact that you're taking these translations too literally (I had the bad habit of doing that too). For example, the first sentence could also be translated to:

涼しくなってきた (lit. It came to be that it's cool)
It has gotten cooler.

Be wary of added/removed nuances in translations. In this case, the translation you provided uses the verb start or the progressive tense to try and convey the feeling of てきた, but the original Japanese sentence doesn't contain neither of these. It doesn't necessarily mean the translation is wrong, because the added manner is a bit irrelevant in this context, but we can say that it's not accurate, at least not accurate enough to represent exactly what is being said in Japanese. The Japanese sentence is very simple and the てきた doesn't tell a lot about the manner of the change, it only gives us the information that it "came" to you, to your senses, etc.

How can I tell if it's something that is still ongoing or if the change is in the past?

With てきた alone, only the context will tell you because it's not the purpose of this construction. Of course, if you absolutely need/want that information, you can add it in Japanese too with other tools, like ところ、始める, etc. Here's another related question.