Under the per se DWI law in New York State, the prosecutor will need to prove that on any given date at a certain location and time that you were operating a motor vehicle when your blood alcohol content was a 0.08 or higher. It is not related to how you were operating the vehicle, how you smelled, how you looked, or how you sounded; it is that your blood alcohol content was over that line.
Common law DWI is almost the opposite of that. It is basically that at a time you were driving that motor vehicle, your ability to operate the motor vehicle was impaired to such a substantial extent that you were unable to operate the motor vehicle as a safe and prudent driver. That is going to be based on a number of things. If you took a test then they can use evidence of a breath test, but generally speaking, it is based on how you looked, how you smelled, how you acted, how you sounded, how you performed on the field sobriety tests, and what admissions you made. It is those types of qualities that they are looking for. Those are going to be the things that they are going to be looking at to decide whether you are worthy of being charged with a common law DWI. If you have decided to take the breath test
Normally if you take the breath test and blow over the legal limit you will be charged with both of the misdemeanor's. If the blood alcohol content was high enough then you will get them charged with an aggravated DWI as well. The threshold for aggravated DWI is a 0.18 or higher. If you get someone that blows a 0.21 then they now have an aggravated per se and common law DWI. Sometimes if your breath test is at the Aggravated level you will end up with being charged with common law DWI, Per Se .08, and Aggravated DWI all as misdemeanor's. In a future post I will explain the sentencing guidelines in New York as they relate to these three charges.