تفاوت used to و would حال به تفاوت used to و would می پردازیم. همانطور که دیدید این دو ساختار موارد استفاده ی مشابهی دارند اما در مورد تفاوت used to و would اما لازم است بدانید که دو تفاوت بسیار مهم و بزرگ با هم دارند. ۱) Would تنها در جملاتی می آید که بازه زمانی گذشته به طور مشخص قبل از would ذکر شود در حالی که برای به کار بردن used to نیازی به آوردن زمان قبل از آن نیست. I used to watch cartoons every day when I was very little. Now I don’t watch TV at all. من قبلا هر روز کارتون تماشا میکردم وقتی کوچک بودم اما الان اصلا تلویزیون نمیبینم. در این مثال بازه زمانی when I was very little در انتهای جمله آمده است اما اگر بخواهیم در همین مثال از would استفاده کنیم درست نیست: I would watch cartoons every day when I was very little. Now I don’t watch TV at all. چون همانطور که اشاره کردیم حتما باید قبل از آوردن would بازه زمانی گذشته را آورده باشیم. اما استفاده از would در جملات زیر کاملا درست است چون بازه ی زمانی مشخص شده و قبل از would آمده است: When I was very little, I would watch cartoons every day. Now I don’t watch TV at all. When I was a student, I used to sleep until 11 on the weekends. وقتی دانش آموز بودم عادت داشتم آخر هفته ها تا ۱۱ بخوابم. ۲) تفاوت مهم دوم این است که would با افعال حالتی آورده نمیشود. برای مطالعه کامل افعال حالتی (state verbs) و افعال کنشی (action verbs) میتوانید به وب سایت مراجعه کنید. افعال حالتی افعالی هستند که یک حالت را بیان می کنند (نه یک عمل را). مثلا در جمله I want an ice cream. من یک بستنی میخواهم. فعل want در واقع اینجا عملی را انجام نمی دهد و تنها یک حالت را بیان می کند. و افعال کنشی افعالی هستند که بیانگر یک عمل هستند. I drink tea every morning. من هر روز چای مینوشم. در اینجا drink نشان دهنده ی یک عمل است. پس ما میتوانیم از used to برای هر دو نوع افعال کنشی و حالتی استفاده کنیم. مانند: I used to play football every Friday evening. من قبلا هر جمعه غروب فوتبال بازی میکردم (فعل play یک فعل کنشی است) I used to think about my mistakes a lot. من قبلا خیلی به اشتباهاتم فکر میکردم (فعل think یک فعل حالتی است.) اما

Okay. I've have googled the question and I think the reason that used to is more correct than would is because used to is for a past action that continued for a length of time. If we talk about working for someone, it is generally a job that continues for an uninterrupted length of time and is not in the category of a repeated action which we do often, such as I would go to the beach with my friends. Hope this answers your question.

Just to clarify Nathan's answer, it isn't so much "action verbs" that use would ("visit", after all, is an action), it is actions that were repeated a number of times. So with the example you give, working for the police officer is a single action. You could however say, "I would work for the police officer in the mornings/regularly/every weekend/" because the action is repeated again and again.

Would is an axillary verb in the past which expresses a wish or desire. Therefore if you use would then it doesn't mean the person actually worked for the police officer in the past. It means he wanted to but didn't for some reason. If that was the case it is more correct to say; " He would have worked for the police officer if he hadn't decided to join the army instead". (for example). However since he actually did work for the police officer but obviously stopped for some reason, it is correct to say; " He used to work for the police officer." which means that he did so some time in the past.

Would is only used with action verbs, used to is used with both action and non-action verbs. I would/used to visit my grandparents every weekend, when I was a child. I used to like broccoli, but I hate it now.