When we use user defined functions in SQL to return a table, why don't we use `BEGIN`and `END`?

e.g. 

```
CREATE FUNCTION Customers
(@minId int)
RETURNS TABLE 
AS
RETURN(SELECT *
    FROM   TrackingItem ti
    WHERE  ti.Id >= @minId)

```

works 

but

```
CREATE FUNCTION Customers
(@minId int)
RETURNS TABLE 
AS
BEGIN
   RETURN(SELECT *
   FROM   TrackingItem ti
   WHERE  ti.Id >= @minId)
END

```

doesn't work