Recently, I was chatting with a refugee from Syria, a young woman with a degree in architecture, who is still learning Portuguese. I happened to say, just en passant, that my secretary is very "eficiente". That non-native speaker immediately asked me why I had used "eficiente": "Could one not say 'eficaz' instead?" I answered "no", and there came the inevitable "why not?"
At that moment, all I could say was that "a person is eficiente" and "a prescription drug is eficaz". It's very easy for a native speaker to say when to use one or the other, but sometimes difficult to explain why. The Priberam offers the following definitions for each adjective:
- Que tem eficácia.
- Que produz determinado efeito.
- Que efetua o que promete ou o que se espera; que causa o resultado inicialmente pretendido.
- Que funciona, produzindo o efeito esperado. = APROPRIADO, EFICAZ ≠ INEFICAZ
- Que tem competência ou reúne as condições e características apropriadas para a consecução de algo. = CAPAZ, COMPETENTE ≠ INCOMPETENTE
- Que tem um desempenho conforme as normas.
- Que obtém resultados ou tem o funcionamento esperado com uma maior economia de recursos e/ou tempo (ex.: o equipamento da fábrica é eficaz, mas pouco eficiente porque gasta muita energia).
Question: Is there a simple, foolproof manner to explain the difference between these two words to a non-native speaker of the Portuguese language?
Addendum: I've seen even native speakers confuse these two words before. Although the answer may be simple and easy to find, I think posting it here will prove useful to our non-native speakers.