I'm the first if you see, 3-in-one if you know, and soon to be three if you observe. What am I?
It could be the
Subject- object - verb trio of a sentence in English (or any language)
I'm (or any word of a normal sentence) is the subject - obviously. And then followed by verb (usually) and then an object. But, in this case they are reversed - a thing you know becomes a subject(3 in one) and once you observe, it is the action/ verb you are talking about.
It is a specially constructed English sentence, without violating rules of grammar.
It could be
I'm the first if you see,
You see the Sun
3-in-one if you know,
As observed from the Earth, a solar eclipse occurs when the Moon passes in front of the Sun.
and soon to be three if you observe.
This occurs when the Sun, Moon and Earth are aligned.
It might be
The Play/Pause/Restart Button on youtube (or other devices/applications).
At first glance
After that, you observe
And at the end,