I recently started reading the book “On Morrison” by Harvard English professor Namwali Serpell, which is a work of literary criticism about the entire oeuvre of the seminal American novelist Toni Morrison. The book came to my attention because it has appeared on many “best of 2026” book lists so far this year.
This book inspired me to write an email about one of the meanings expressed by the preposition “on”—because, in addition to the book’s title, the title of its preface is also a prepositional phrase with “on”: “On Difficulty.” Every subsequent chapter is also essentially a long essay “on” a particular work in the writer’s oeuvre.
If you have taken our foundational grammar course “Core Concepts of English,” you would know that prepositional phrases are modifier phrases that start with a preposition—like “on”—and are completed by nouns or noun phrases—like “Morrison,” “difficulty,” or “the bus.”
You might also remember that, as modifier phrases, prepositional phrases can express meanings in essentially three different ways:
First, phrases with a particular preposition have a range of relational meanings that they can express by themselves with their noun phrases. For example, one of the relational meanings that the preposition “on” expresses with the noun phrase after it is “spatially on top of something.” In “the book is on the table,” the prepositional phrase “on the table” expresses the meaning of “spatially on top of the table” by itself.
Second, prepositional phrases can express fixed meanings as fixed expressions by themselves. For example, the expression “on duty”—meaning “working at that time”—is a fixed expression with the preposition “on.” There is no need to think about the relational meaning between “on” and the noun “duty” here—this is simply a fixed prepositional phrase with a fixed meaning.
Third, certain verbs, in order to express specific meanings, have the structural characteristic of requiring a prepositional phrase with a specific preposition. For example, when the verb “depend” needs to express the “recipient” of this “dependence,” it has to be completed by a specific prepositional phrase with “on,” such as “on you”: “We are depending on you.”
Now, let’s go back to the prepositional phrase that forms the title of the book, “On Morrison.”
Can you tell which “category” of meaning this prepositional phrase is expressing here?
It is the first type outlined above. Namely, one of the relational meanings that the preposition “on” can express with the noun phrase after it is the figurative meaning of “about that noun phrase” or “pertaining to that noun phrase.”
In other words, the prepositional phrase “On Morrison,” as a book title by itself, tells the reader that “this book is going to elucidate the works of the writer Toni Morrison.” Similarly, the title of the preface, “On Difficulty,” expresses by itself the meaning that “this chapter is going to explain the concept of ‘difficulty’ in Morrison’s works.”
As such, “On Morrison” is a very apt title for this book of literary criticism.
If we were to put this prepositional phrase back into a full clause or sentence as a modifier, we could say, for example:
Namwali Serpell wrote a book of literary criticism on Toni Morrison’s works.
Can you form another sentence with a prepositional phrase containing “on” that expresses this same meaning?
最近，我開始閱讀哈佛英文系教授 Namwali Serpell 所寫的《On Morrison》。這是一本評論美國重要小說家 Toni Morrison 全部作品的文學評論著作。我會留意到這本書，是因為它至今已經登上了不少「2026 年度最佳書籍」名單。
這本書令我想到，可以寫一封電郵，介紹介詞 on 所表達的其中一個意思——因為除了書名之外，這本書序言的標題 “On Difficulty” 也是一個包含 on 的介詞組。之後的每一章，也基本上都是一篇「on」這位作家某一部作品的長篇文章。
如果你修讀過我們的基礎文法課程《Core Concepts of English》，應該會知道介詞組是以介詞——例如 on——開首，並由名詞或名詞組——例如 Morrison、difficulty 或 the bus——完成的修飾語詞組。
大家可能也記得，作為修飾語詞組，介詞組基本上可以透過三種不同方式表達意思：
第一，某個介詞，本身可以跟它後面的名詞組表達不同的「關係性」意思。例如，介詞 on 跟其後的名詞組所表達的其中一個關係性意思，就是「在某件事物上面」的空間意思。在 “the book is on the table” 這句中，介詞組 “on the table” 自己就表達了「在桌子上面」的關係性意思。
第二，很多介詞組本身是固定用語，會表達固定的意思。例如，on duty 這個固定用語——意思是「當值中」——就是一個包含介詞 on 的介詞組。在這裏，我們不需要思考 on 跟名詞 duty 之間的關係性意思——它只是一個具有固定意思的固定介詞組用語。
第三，某些動詞在表達特定意思時，在結構上必須由包含某個特定介詞的介詞組完成。例如，當動詞 depend 需要表達「依賴」的「對象」時，就必須由包含 on 的特定介詞組完成，例如 “We are depending on you” 中的 “on you”。
那現在可以回到構成這本書書名的介詞組 “On Morrison”。
你能不能分析出，這個介詞組在這裏表達的是哪一個「類別」的意思呢？
它表達的是上面所說的第一類意思。具體來說，介詞 on 跟其後的名詞組可以表達的其中一個關係性意思，就是「關於這個名詞組」或「跟這個名詞組有關」的抽象意思。
換句話說，介詞組 “On Morrison” 本身作為書名，就很清晰地告訴讀者「這本書是『關於 Morrison』的，會解釋她的作品」。同樣，序言的標題 “On Difficulty” 本身表達的意思，就是「這一章是關於『difficulty』的，會解釋 Morrison 作品中『difficulty』這個概念」。
因此，《On Morrison》是一個非常貼切的文學評論書名。
如果我們把這個介詞組放回一個完整子句或句子中作為修飾語，可以例如：
Namwali Serpell wrote a book of literary criticism on Toni Morrison’s works.
Namwali Serpell 寫了一本關於 Toni Morrison 作品的文學評論著作。
你能不能使用一個包含 on、並表達跟這裡同一個意思的介詞組，組成另一個句子呢？