<p>Yeah i got another question about conjunctions. When you combine two independent clauses (or just any clause) with conjunction and a comma, both parts of the sentence needs to have a subject and a verb right? For example "Tony studied physics, and he used what he learned on his job." would it also be correct to say "Tony studied physics, and used what he learned on his job?"</p>
<p>When you attach an independent cause to a sentence you need a semi-colon. When you attach a dependent clause, you need a comma.</p>
<p>Yes both of your sentences are correct. I believe using "and" would necessitate a comma in your specific case. So saying, "Tony studied physics; he used what he learned on his job" would also be correct.</p>