If I had studied harder <ㅡㅡ> If I had studied hard
What is the difference between them?
The only obvious difference is whether to use the positive form of the adjective "hard" or its comparative form "harder."
With the positive form, the meaning is obvious.
If you use the comparative form "harder," I would be waiting for you to complete the comparison --> harder than what?
http://guidetogrammar.org/grammar/adjectives.htm
Scroll down and read about Degrees of Adjectives
The difference between "If I had studied harder" and "If I had studied hard" lies in the use of the adverb "harder" in the first sentence. In this context, "hard" is an adjective that means "with great effort or vigor." In the second sentence, "hard" is an adverb that simply describes the manner in which the studying was done.
To understand the difference, let's break down the grammar. Both sentences are in the form of conditional sentences, specifically the third conditional, which expresses a hypothetical situation in the past and its imaginary consequences.
1. "If I had studied harder" suggests that the person believes they didn't put in enough effort in their studies. The addition of the adverb "harder" indicates that they could have put in more effort than they actually did. This sentence implies that the person feels they could have achieved better results if they had applied more diligence or intensity to their studies.
2. "If I had studied hard" suggests that the person believes they put in some effort during their studies, but not necessarily as much as they could or should have. This sentence implies that the person acknowledges their past study efforts but wonders whether putting in more effort would have produced better outcomes.
In summary, "If I had studied harder" implies potential regrets about not putting in enough effort, whereas "If I had studied hard" suggests a questioning of the level of effort they had already put in and its potential impact on the outcome.