No lo eran

[Tyrn]

Hi,

Si sus lágrimas de un momento antes habían sido calculadas, ésas no lo eran.

Curiously, I have no trouble understanding the sentence. I just can't explain to myself, why lo is necessary, and if it is, why lo and not something else

[wrholt]

"lo" refers to the phrase "(habían sido) calculadas", which is what the previous tears were but what the current tears are not.

We could translate this sentence as "If his/her tears of a moment before were/had been calculated, those were not (that/it)". In English we typically would not use a pronoun in the clause "those were not". However, in Spanish it is almost obligatory to use an explicit complement or an explicit direct object pronoun with "ser".

When the direct object pronoun refers to a specific noun, the object pronoun has the same gender and number as the noun it refers to. But when the direct object pronoun refers to something that is NOT a noun, one must use the neuter direct object pronoun "lo", which happens to have the same form as the masculine singular direct object pronoun.

[AngelicaDeAlquezar]

I agree with wrholt.

If you say "[...] ésas no eran", then it's expected that you say what they were not. The use of "lo" makes the meaning explicit: "Those tears are not false".