Breakdown of O médico mandou que eu substituísse o pão por mais fibra.
eu
I
o médico
the doctor (m)
o pão
the bread
mais
more
por
through / by / for / because of
que
that (conjunction)
mandar
to order
substituir
to replace
a fibra
the fiber
Questions & Answers about O médico mandou que eu substituísse o pão por mais fibra.
Why is substituísse used here instead of a normal past tense?
This sentence is reporting a command given in the past. If the doctor were speaking directly to you, they would use the imperative: "Substitua o pão!" (Replace the bread!). When you report that command later using a past-tense reporting verb like mandou (ordered), that imperative command shifts into the imperfect subjunctive (substituísse).
We translate this as "replace bread with more fiber". Why does the Portuguese sentence use por instead of com?
In English, we usually replace something with something else. In Portuguese, the verb substituir requires the preposition por. Think of it as trading or substituting the bread for (por) more fiber. Using com here is a common mistake for English speakers, but it sounds unnatural in Portuguese.
Why does substituísse have an accent mark? The infinitive substituir doesn't.
In the imperfect subjunctive, the spoken stress always falls on the vowel just before the -sse ending. For this verb, that's the i. Because the u and the i are pronounced as two separate vowel sounds right next to each other (called a hiatus), Portuguese spelling rules require an acute accent on the í to show that it carries the stress.
Could I say disse que instead of mandou que?
Yes, you could say O médico disse que eu substituísse... (The doctor told me to replace...). Both verbs will trigger the imperfect subjunctive when they are used to report a past command. However, mandou (from the verb mandar) is a stronger word; it specifically means "ordered" or "commanded," making it very clear that the doctor wasn't just giving a casual suggestion.
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