Correct

得 vs 必须

/ děi vs bìxū /
Strokes

Formula

1
非 + 得
2
必须 + 得

Definition

得 vs 必须 both are Auxilliary Verbs, which means [must; have to; be bound to].

Example

得 vs 必须 both means "must; have to"; 得 is very colloquial, while 必须 is more literary and forceful.
In such sentences the two words are interchangeable, but they are of different styles. 必须 carries a commanding tone。
1
shāo
发烧
le
  
,
de
  
(
必须
  
)
yuàn
医院
  

You have to go to hospital for you have got a fever.

2
děi
  
(
必须
  
)
努力
xué
学习
  

I had to work hard.

3
Zhège
这个
rènwu
任务
men
你们
必须
zài
liǎng
yuè
nèi
wánchéng
完成
  

You must finish the job in two months.

In very colloquial and casual speech, 得 is used more often than 必须 (especially in North China).
4
kǒu
口渴
  
,
děi
kǒushuǐ
口水
  

I am thirsty,and I must go to have a drink.

5
Zhè
shì
děi
zài
xiǎngxiǎng
想想
  

I'd like to think about it again.

得 vs 必须 both means "to need", and are followed by a numeral-classifier or such a compound plus a noun as the object.
6
Zhuāngxiū
装修
zhè
tào
fáng
房子
  
,
de
  
(
必须
  
)
wàn
几万
kuài
  

The decoration of the house will cost you at least thousands of Yuan.

7
Zhè
xiàng
rènwu
任务
de
  
(
必须
  
)
sān
tiān
shíjiān
时间
cái
néng
wánchéng
完成
  

The task must be finished in three days.

得 can also indicate "asurmise" and be preceded by 非, 必须 cannot be so used.
非 + 得 必须 + 得
8
zhème
这么
yònggōng
用功
  
,
de
0
0
fēn
  
!

You are likely to get zero mark if you are not industrious.

9
Zhège
这个
qiúyuán
球员
  
,
de
chī
hóngpái
红牌
  

The player is likely to get the red ticket.

10
Zhème
这么
ài
chī
tiánshí
甜食
  
,
jiānglái
将来
fēiděi
非得
pàng
发胖
  
!

She is likely to be fat in the future if she takes so much sweet food.

The negative form of the two words is unusual. The negative form of 得 is 不用, 用不着; that of 必须 is 无须, 不须, 不必.
11
Zhuāngxiū
装修
zhè
tào
fáng
房子
yòngbuzháo
用不着
3wàn
3万
yuán
  

The decoration of the house will cost less than 30,000 yuan.

12
Zhè
xiàng
rènwu
任务
3
3
tiān
shíjiān
时间
jiù
néng
wánchéng
完成
  

It takes less than 3 days to finish the task.