Which is correct? 1) or 2)?

Both, although using 'you' like that is relaxed/casual/conversational/informal and not suitable for more formal or written English.

My attempt to make it formal. Please comment it:

regress:

1) reasoning involved in the process in which one assumes the conclusion is true and reasons backward to the evidence.

2) the reasoning involved when one assumes the conclusion is true and reasons backward to the evidence

Does it work? If not, please make one.

Fine.