Take a sentence such as "He should take the bus." It has at least three different meanings, or possible emphases or shades of meaning, if you like.
a) If I want describe someone's expected movements, I might say, "He's not home yet because he'll be at work till 6, but after that he should take the bus home." Here, "should" indicates that that's X's usual practice, the norm, what's to be expected. "The bus should be here in five minutes," is another example of this sort.
b) On the other hand, "should" can also indicate the preferable course of action. "He should take the bus because it's quicker than walking, cheaper than the train," etc.
c) But we can also use "should" in a specifically moral sense. "He should take the bus because it's kinder to the planet than driving."
How sharp are these distinctions? In English we don't need to think about it, because we can say "He should take the bus" in all three cases. In Japanese, however, these require three distinct grammar constructions:
a) 彼はバスを乗るはずです。kare ha basu wo noru hazu desu.
b) 彼はバスを乗る方がいい。kare ha basu wo noru hou ga ii.
c) 彼はバスを乗るべきです。kare ha basu wo noru beki desu.
Of course, it's attractive to be able to make fine distinctions, and it's certainly good to be made to think about distinctions that one's native language tends to gloss over. How much of our sense of what is morally right derives from our sense of what is prudent and/or natural? Japanese makes you think about that - at least, if you are me.
On the other hand, Japanese speakers and English speakers (at any rate UK ones) alike love vagueness and ambiguity, particularly when it comes to ascribing motives, and in this case English is preferable for that important purpose.