"Not all" versus "all are not"

There is a clear difference in meaning between

All X are not Y.

and

Not all X are Y.

The first statement, taken literally, says that no member of group X has attribute Y.

Most people don't mean it that way, but by using that construct, they sow confusion.

If you mean that only some members of group X have attribute Y, while some do, then say that:

Not all X are Y.

If you mean that zero members of group X have attribute Y, then please use a different construct:

No X are Y.