"Γιατί πρόσθεσες αλάτι;"

Translation: Why did you add salt?

[LewieHayes]

"To season the food, silly!"

[Fernando757203]

"πρόσθεσες" is from "Προσθέτω", is an irregular past ?

[troll1995]

No, that's regulal, I think.

[Fernando757203]

why "τ" from "Προσθέτω" becomes "σ" in past ?

[robert672165]

what troll meant was that, since consonants change according to rule in the past, it's regular. τ becomes σ as a rule. These aorist consonant changes are given in "tips & hints" for "past 1"

[Fernando757203]

Thanks for your answer.
But "τ" becomes "σ" is not given in tips for past 1.