SAT Grammar: When to Place a Comma Before Conjunctions

Some grammar questions ask you to determine whether a comma must be placed before a conjunction or not. To accurately answer this pattern of questions, you should fully understand the classification of conjunctions and their rules.

Two Types of Conjunctions

Conjunctions can be divided into two main types:

• Coordinating conjunctions
• Subordinating conjunctions

To decide whether a comma is needed before a conjunction, it’s important to understand these two types clearly. Before we look at the rules for using commas, let’s briefly review what each type of conjunction does.

Coordinating Conjunctions

As the name suggests, coordinating conjunctions connect two independent clauses. They are often remembered by the acronym FANBOYS, which stands for,

• For
• And
• Nor
• But
• Or
• Yet
• So

These conjunctions have two important characteristics:

1. They are generally not used at the beginning of a formal sentence (though this is fine in conversation or informal writing).
2. They usually require a comma before them when linking two independent clauses.

Here are some examples of sentences with a coordinating conjunction.

The students enrolled in the advanced robotics course must complete a final project, and their performances will be evaluated by a panel of engineers from local universities.

In this sentence, the coordinating conjunction “and” connects two independent clauses. Because it links two complete thoughts, a comma is placed before it.

The committee’s decision to fund the project was influenced by data showing a decline in water quality, yet the measure won’t take effect by the end of next year.

Here, “yet” is another coordinating conjunction. It contrasts two ideas, one about the committee’s decision and the other about the delay in action.

On the digital SAT, you will see a following question of this topic.

Materials scientist Dr. Aisha Nouri and her research team set out to improve the durability of a widely used aerospace alloy known as TiAlV, a blend of titanium (Ti), aluminum (Al), and vanadium (V), by substituting vanadium with molybdenum ______ early simulations suggested that this new composition, TiAlMo, might enhance resistance to fatigue and high-temperature stress, but experimental results revealed structural weaknesses under repeated mechanical load.

Which choice completes the text so that it conforms to the conventions of Standard English?

(Mo), and

(Mo) but

(Mo), yet

(Mo)

None

Time's up

Coordinating Conjunction without Comma

However, in some sentence structures, you don’t need to place a comma before a coordinating conjunction. This happens under the following condition:

On the digital SAT, you may sometimes encounter a question where the answer choices include the same conjunction: with and without a comma.

When this happens, check whether the subject of the second clause is omitted. If both clauses share the same subject and the second one is left out, then a comma before the conjunction is not required.

Let’s try the following SAT practice problem of this pattern.

Before the widespread adoption of digital photography, most cameras relied on 35mm film, a format introduced in the 1930s. Film photography remained dominant throughout the twentieth ______ became obsolete in the late 1990s.

Which choice completes the text so that it conforms to the conventions of Standard English?

century but

century,

century that

century, but

None

Time's up

Subordinating Conjunctions

Subordinating conjunctions are conjunctions that introduce a dependent clause and connect it to an independent clause. Roughly speaking, any conjunction that is not one of the FANBOYS is considered a subordinating conjunction.

Here are some common subordinating conjunctions:

• Though
• Although
• While
• If
• Since
• Because

A subordinating conjunction can appear in two positions within a sentence:

1. At the beginning of the sentence
2. In the middle of the sentence

When a subordinating conjunction comes at the beginning, the first part of the sentence becomes a dependent clause, which is followed by an independent clause after a comma.

While the brown rat (Rattus norvegicus) can produce several litters each year, leading to populations in the millions, the slow-breeding Sumatran orangutan (Pongo abelii) often exists in groups of fewer than a dozen individuals in the wild.

In this sentence, the subordinating conjunction “while” appears at the beginning of the sentence. This creates a structure in which a dependent clause is followed by an independent clause, separated by a comma.

• Dependent clause: While the brown rat (Rattus norvegicus) can produce several litters each year, leading to populations in the millions

• Independent clause: the slow-breeding Sumatran orangutan (Pongo abelii) often exists in groups of fewer than a dozen individuals in the wild.

Next, let’s move the subordinating conjunction “while” to the middle of the sentence.

The brown rat (Rattus norvegicus) can produce several litters each year, leading to populations in the millions while the slow-breeding Sumatran orangutan (Pongo abelii) often exists in groups of fewer than a dozen individuals in the wild.

In this version, the first part of the sentence is the independent clause, and the latter part is the dependent clause. When a subordinating conjunction like “while” appears in the middle of a sentence, no comma is used between the two clauses.

• Independent clause: The brown rat (Rattus norvegicus) can produce several litters each year, leading to populations in the millions

• Dependent clause: while the slow-breeding Sumatran orangutan (Pongo abelii) often exists in groups of fewer than a dozen individuals in the wild.

Practice Questions

Question 1

The daily activity patterns of owl species vary significantly across habitats and regions. The eastern screech owl (Megascops asio), for example, is nocturnal—it hunts small mammals at night and remains hidden during daylight hours. In contrast, the burrowing owl (Athene cunicularia), which lives in open grasslands, displays a more flexible schedule. It often forages in the early morning and late afternoon, with occasional nighttime activity. These contrasting behaviors reflect evolutionary adaptations to different environments ______ they also highlight the diversity of survival strategies among birds of prey.

Which choice completes the text so that it conforms to the conventions of Standard English?

, whereas

, whereas,

whereas,

whereas

None

Time's up

Question 2

Artificial intelligence has rapidly entered the field of medicine, particularly in diagnostics. AI-powered tools can now detect tumors in medical images with an accuracy that rivals, and in some cases exceeds, that of experienced radiologists. These systems are already being used in hospitals across several countries. Not all experts are enthusiastic about this shift ______ they caution that overreliance on machine learning could lead to diagnostic errors if the systems are not carefully monitored and regularly updated.

Which choice completes the text so that it conforms to the conventions of Standard English?

, but

but,

but

, but,

None

Time's up