Question

How to differntiate between harsh sounding words and plesant sounding words?

Answer 1

Euphonious words are those with pleasant sounds, and cacophonous words are ones which sound harsh.

Words that have positive and/or pleasant meanings tend to sound pleasant. This is not grammar, but probably a characteristic of nature.

Incidentally, the word harsh as in "cacophonous words are ones which sound harsh" has both mechanical as well as semantic significance.

Also, how you perceive a word could also be mostly subjective. The pronunciation, the spelling, the visual of the word may bring about differing opinions about it being euphonious or cacophonous.

It isn’t always wholly subjective though; perception is the key.