French is very confusing, I get it. Even still, we have to learn these types of things. The reason CER and GER are irregular is because they have a different sound due to the fact they have e, or an i at the end. For example, manger without the -e would make a hard g sound. Same thing for -cer verbs. so for the following conjugations: -ais, -ait, -aient, you need to add the e back into the verb for -ger verbs. For -cer verbs though, you need to add an accent cedille (ç).
Example: Je Mange -> Je Mangeais | Je Commence -> Je Commençais
NOTE: This rule does not apply to -IR Verbs due to the fact they always start with an I, which makes the soft sounds.
These are irregular verbs due to wrong conjugations. (ex: sommes =/ sommais | etes = etais)
