Learn French: Le verdict aurait changé si la défense avait utilisé celle-ci. - The verdict would have changed if the defense had used this one.

This sentence uses the Third Conditional to talk about an unreal, imaginary situation in the past. The rule is: the main result is in the past conditional (aurait changé - would have changed), while the condition following si is in the pluperfect (avait utilisé - had used).

Why does the sentence use celle-ci instead of ça or ceci for "this"?

Ça and ceci are used for general ideas, statements, or undefined things. Celle-ci (this one) is a demonstrative pronoun that points back to a specific feminine singular noun that was already mentioned in the conversation, such as la preuve (the piece of evidence) or la tactique (the tactic).

Can I put the si part at the beginning of the sentence?

Yes! You can completely swap the two halves without changing the meaning: Si la défense avait utilisé celle-ci, le verdict aurait changé. Just remember to add a comma after the si clause when it comes first.

How exactly is the past conditional aurait changé formed here?

It is formed by taking the conditional present of the auxiliary verb avoir (aurait) and adding the past participle of the main verb (changé). It matches the English structure perfectly: "would" (-ait ending) + "have" (aur- stem) + "changed" (changé).