Questions & Answers about По-моему, это хорошая идея.
Why use по-моему instead of a dative pronoun like мне, since the current lesson focuses on мне?
While your current lesson teaches you to use the dative for physical or emotional states like мне холодно (I am cold), you cannot use мне to state an opinion like 'in my opinion'. For that, you need the fixed expression по-моему.
Why is there a hyphen in по-моему?
It is a standard spelling rule in Russian: adverbs that start with the prefix по- and end with -ому or -ему are always written with a hyphen.
Since идея is a feminine noun, why does the sentence use the neuter word это instead of эта?
When это is used as the subject of a sentence to mean 'this is' or 'that is', it stays frozen in the neuter form. You would only use the feminine эта if it were directly attached to the noun, like in the phrase эта хорошая идея (this good idea).
How would I change this sentence to say 'this was a good idea'?
In the present tense, Russian drops the verb 'to be'. However, just like the impersonal expressions in your current lesson, you must add the verb back for the past tense. Because идея is a regular feminine noun, you would use была rather than the neuter было, making it по-моему, это была хорошая идея.