What's the difference between ending an adjective with -o and with -eco

Question

What would be the difference between ending adjectives with -o and with -eco? For example, between saying kolero and kolereco or feliĉo and feliĉeco.

Answer 1

Ruĝo means ”red (color)” and ”ruĝeco” means ”redness”. Imagine we are looking at a painting. I could say ”Mi ŝatas ĝian ruĝon” because I think the color is beautiful, but that does not necessarily mean I think the color suits this painting, or that I enjoy the manner in which the color was used in this case. On the other hand I could say ”Mi ŝatas ĝian ruĝecon” because I think the use of the color creates an impressive effect, even if I was to hate the color red.

A common case where you need to pay attention is with ”rapid-”. Rapido means ”speed” and rapideco means ”quickness”. Every animal has a maximum ”rapido”, even a turtle, but fewer have ”rapideco”.

La rapido de lumo estas 300 000 km en horo.

Homaj haroj kreskas per averaĝa rapido de unu centimetro en monato.

La rapideco de la leopardo estas nekredebla.

Other adjective roots don’t make such clear distinction between endings. Feelings cannot exist without somebody feeling them, so it does not make alot of sense to try and separate the two versions. I believe ”Feliĉo” is the feeling of happiness itself, while ”feliĉeco” is the state of being happy.

It is simpler with non-adjective roots. Their -o versions are already ”occupied” so you can always use ”eco”.

Vi estas amata. Vi estas amato. Via amateco estas ĵaluziga.