Could you please rephrase your explanation, I didn't understand ? — Merkwurdichliebe
Ok.
If you can assume the truth or falsity of X, then X must be able to be true or false. This means X is 'truth apt', where there are conditions under which it is true, and conditions under which it is false. If 'X' is 'It is raining here now' (for here, now being my location), X is true just when it is raining and false just when it is not raining. 'It is raining here now' is the kind of expression that can be true or false.
Consider 'Get me some water please', it is a request, it is not a statement of fact
even if it is an expression of desire. 'Get me some water please' is never true or false, since it is a request. Therefore, since it can't be true or false, assuming it is true cannot help you interpret it.
Consider 'In Heaven I am a wild ox, in Earth I am a lion', on the face of it it could be true or false; it's true just when the person saying/writing it
really is a wild ox in Heaven but also
really is a lion on Earth. and false when one or both of these these conditions does not occur. But, assuming the truth or falsity of it does not help you interpret it one bit. The use of language is figurative, allegorical, metaphorical and so on, the literal truth doesn't matter a drop. What does matter is how it functions in its own context as a metaphor.
]Do we dare to open
Our minds and souls to even
Analyze it? Or should it rest in
Secrecy? All I know is that I can't
Deny its licentious attraction,
So I want the spirit to speak.
"In heaven I am a wild ox.
On earth I am a lion.
A jester from hell,
And the shadows almighty.
The scientist of darkness
Older than the constellations.
The mysterious jinx and
The error in heavens master plan." — Vintersorg, the Enigmatic Spirit
There's no way someone would ever come up with the context of a song about a spirit that fled from heaven because it felt powerless there. In Heaven, the spirit was just an angel among angels, on Earth, it was a mighty predator of unfathomable intelligence and significance. It chose to sacrifice the vulnerable ecstasy of heaven for the power it would have in the mortal realm. The principle of charity isn't going to give you that, because the truth conditions of the statement 'In Heaven I am a wild ox, on Earth I am a lion' provide little to no information about its sense outside of the context of the song.
Edit: even within the song, it's uttered as a metaphor which summarises the reasons why the spirit fled from heaven and its opinion of Heaven and humans. You can 'assume it is true for the spirit' in a sense, but notice that it doesn't actually matter whether the spirit really was a wild ox in Heaven and transformed into a lion on Earth, what matters is the two symbolic dyads of wild ox/lion prey/predator interacting with the other dyad of Heaven/Earth.
Of course, when my friend told me he prefers to hang around with people dumber than him because 'on Earth I am a lion', I understood, because we both knew the song.