都是用来表示缺少、短缺，"lack", "lack of" 和"a lack of"之间有什么区别呢？"owing to lack of patriotism"， "owing to a lack of patriotism" 和"owing to lack patriotism" 哪一个才是正确的表达方法呢？

首先我们需要注意的是，lack找个词既是名词也是动词。名词意思是“the state of not having sth or not having enough of sth 缺乏；匮乏；短缺”；动词意思是“to have none or not enough of sth 没有；缺乏；不足；短缺”。

因此，我首先需要确定的是lack是用作动词还是名词。lack作动词时是及物动词，固定的用法是lack sth，不可用于被动语态。例句如下：

Some houses still lack basic amenities such as bathrooms.
有些住宅仍没有像卫生间这样的基本设施。

What we lack in this house is space to store things.
我们这所房子缺少的是储物空间。

We are lacking three members of staff due to illness.
我们有3人因病缺席。

lack用作名词时，常见搭配是lack of sth，与shortage是同义词。让人疑惑的地方在于，lack是不可数名词，但是a lack of却是常见用法，而lack of也是对的。如以下几个例句（摘自剑桥词典）所示。

Her only problem is a lack of confidence.
她唯一的问题是缺乏自信。

Lack of sleep had made him irritable.
睡眠不足令他烦躁易怒。

If he fails it won't be for/through lack of effort (= he has certainly tried).
他若失败了，那肯定不是因为他努力不够。

那么，a lack of和lack of到底有什么差别呢？thefreedictionary中对名词lack的定义如下：

1. Deficiency or absence: Lack of funding brought the project to a halt.

2. A particular deficiency or absence: Owing to a lack of supporters, the reforms did not succeed.

从中我们可以看出，lack of 前面加冠词a表示在特定某方面的欠缺，不加冠词时表示一般性的欠缺或缺少。所以，开头那个问题的正确答案是“Owing to a lack of patriotism”。