The main difference is that **tornar-se** has more focus on the transformation (but not necessarily with some progressive aspect), whereas **ficar** focuses on the final state. Remember that *tornar* can also be used in a similar way to "to turn" in sentences such as "ele tornou esta empresa numa das mais sucedidas no ramo". As you may imagine, this still leaves quite a margin for overlap. I assume you're referring to _become_ in the OED sense 5. Let's look at the definition and the examples: > 5. To come to be (something or in some state). > > ✝ a. with _to_, _into_. _Obs._ [...] > > b. with _subst._ or _adj. complement_. > > * [...] (too old for me to understand) > * _c_ **1350** _Wilt. Palern._ 881 881 He cast al his colour and bicom pale. > * **1398** TREVISA _Barth._ _De P. R._ v. lxii. (1495) 178 Goddis sone bycame man and dwellyd among us. > * **1483** CAXTON _Gold. Leg._ I35/4 So wyse a man is such a fole becomen. > * **1549** _Compl. Scot._ 2 The universal pepil ar be cum distitute of Justice. > * **1611** BIBLE _Gen._ xix. 26 His wife looked backe .. she became a pillar of salt. > * **1625** BACON _Ess._ (Arb) 479 Their Boughs were becommen too great. > * **1717** LADY M. W. Montague _Lett._ II. xlvi. 30 The asmack, or Turkish veil, is become .. agreeable to me. > * **1774** CHESTERF. _Lett._ I. ii Unfortunately for her, she became in love with him. > * **1810** HENRY _Elem. Chem._ (1840) II. 699 When .. more largely diluted with water, it becomes hot. > * **1848** MACAULAY _Hist. Eng._ 1. 4 When first they became known to the Tyrian mariners. > * **1876** GREEN _Short Hist._ vi. §4. 298 Florence .. became the home of an intellectual Revival. Note that these are historical citations and some of these sentences use the auxiliary "to be" instead of "to have". I think the distinction between *something* and *state* that the dictionary does can help us. With _becoming **something**_, _torna-se_ will usually be the right word; and for _becoming **some state**, _ficar_. So in Portuguese: * Ele perdeu toda a sua cor e ficou pálido. _("tornou-se pálido" would mean "tornou-se uma pessoa pálida", so a more permanent change)_ * Pouco depois, Goddis tornou-se homem e viveu entre nós. * Um homem tão sábio tornou-se tão tolo. * O (?) universal ficou destituído de justiça. * A sua mulher olhou para trás .. tornou-se uma estátua de sal. * Os seus ramos (?) tinham-se tornado grandes demais. _("tinham ficado" is also possible, but I see here a gradual process where the boughs get bigger and bigger)_ * O véu turco tornou-se .. aceitável/adequado para mim. _(the original has the present participle, which suggests it was a process. Actually you could never use "ficar" here. At some point something is acceptable or it isn't -- so you would use "ser"; it can become acceptable through time though, and then you would use "tornar-se")_. * Infelizmente para ela, ficou apaixonada por ele. * Quando mais diluído em água, fica quente. _(or "torna-se", if we want to focus on the process)_ * Quando os marinheiros de Tiro ficaram pela primeira vez familiarizados com eles. * Florença ... tornou-se o lar de uma renascença intelectual.