Problem: I need to convince my mom to lend me some money for a car down payment.

Difficulties:

1. I've not been very good about paying her back in the past (not a good record).
2. She will need convincing that I need a new car.
3. She doesn't trust my word.
4. I've wasted lots of money in the past.
5. I have had huge credit card debt.

My major points:

1. I'm working a steady job and actually saving some money each month.
2. I'm willing to pay her back with interest.
3. I'm willing to put this in writing.
4. I'm no longer hanging out with folks who lead me astray.
5. I've almost paid off my credit cards.
6. Perhaps another example of how I've changed?

For a good argument, you ANTICIPATE the reader's objections and you ANSWER honestly each one.

Think of your rhetorical stance: you do not AGREE with your opposition but you COUNTER those points.

For example:

Do not say: "I know that I never paid you back before, that I kept money you gave me and idn't use it on the stuff I told you that I needed, so, of course, you don't trust me and you probably shouldn't."

Why not say this? You don't need to remind her of the specific dtails of your failings, and you don't want to agree with her reluctance to help you.

What to say: "I know that I haven't always been responsible in the past, but I assure yo that I've changed. I don't use credit cards anymore, I save a little each paycheck, and I pride myself on my honesty.

Why say this? It focuses on your character not on your mother's doubts.