Is “to” a Preposition or a Conjunction? Understanding the Role of “is to” in English Grammar
When learners encounter the phrase is to in sentences such as The meeting is to start at nine or She is to submit the report tomorrow, a common question arises: does to function as a preposition, a conjunction, or something else entirely? The short answer is that to in the construction is to is neither a preposition nor a conjunction; it is part of the verb phrase be to, which expresses obligation, intention, or scheduled action. To fully grasp why, we need to examine the different grammatical jobs that to can perform, see how is to fits into the verb system, and clarify why it never acts as a conjunction.
Easier said than done, but still worth knowing.
1. The Many Faces of “to”
The word to is one of the most versatile elements in English. Depending on the context, it can serve as:
| Function | Typical Pattern | Example |
|---|---|---|
| Preposition | to + noun/pronoun | *She went to the market.Also, * |
| Infinitive marker | to + base verb | *He wants to learn Spanish. * |
| Particle in phrasal verbs | verb + to + … (less common) | *They looked to the leader for guidance. |
Notice that in none of these roles does to connect two clauses of equal grammatical weight, which is the defining job of a conjunction (e.Day to day, g. Which means , and, but, because). Instead, to either relates a verb to its object (preposition) or signals the infinitive form of a verb (infinitive marker) Worth keeping that in mind..
2. “to” as a Preposition
When to precedes a noun phrase, it functions as a preposition indicating direction, destination, recipient, or limit.
- Direction/Movement: The cat jumped to the windowsill.
- Recipient: I gave the book to my sister.
- Limit/Extent: The temperature rose to 30 °C.
In these cases, to introduces a complement that completes the meaning of the preceding verb or adjective. The prepositional phrase can often be replaced by another preposition without changing the core structure: She went into the market (different preposition, same syntactic slot) No workaround needed..
3. “to” as an Infinitive Marker
The second major role of to is to mark the bare infinitive of a verb. Here, to does not convey meaning on its own; it simply signals that the following verb is in its infinitive form.
- She hopes to travel next year.
- They need to finish the report.
- It is important to listen carefully.
When to appears before a verb, the combination to + verb behaves like a single unit (the infinitive phrase) that can act as a noun, adjective, or adverb within the sentence. Take this: To err is human uses the infinitive phrase as the subject Worth keeping that in mind..
4. The Verb Phrase “is to”
Now consider the sequence is to. This consists of:
- The verb be in its present‑tense third‑person singular form (is).
- The infinitive marker to followed by a base verb.
Together, be to forms a modal‑like construction that conveys:
- Obligation or duty (often formal or scheduled): The president is to address the nation at 8 p.m.
- Intention or plan (especially in news reporting): The team is to launch the new product next month.
- Fate or inevitability (in literary or hypothetical contexts): If the treaty is to succeed, both sides must compromise.
Because be is a verb, the whole string is to [verb] functions as a verb phrase, not as a prepositional phrase or a conjunctive link. The to here retains its role as an infinitive marker; it is not relating a noun to another noun, nor is it joining two clauses Worth knowing..
4.1. Why “is to” Is Not a Preposition
A preposition must be followed by a noun phrase (or pronoun) that serves as its object. In is to, the word after to is a verb (the base form), not a noun. Which means, the preposition test fails:
- ❌ She is to the store. (nonsensical)
- ✅ She is to go to the store. (here to go is infinitive; to the store is a separate prepositional phrase)
4.2. Why “is to” Is Not a Conjunction
A conjunction connects two syntactic units of equal rank—two nouns, two verbs, two clauses, etc.That's why —and often expresses a logical relationship (addition, contrast, cause, etc. In real terms, ). In is to, there is only one clause being expressed; the to does not link anything to another element Most people skip this — try not to..
- She is to [something] and [something else]
But such a pattern does not exist in standard English. The to in is to never coordinates two independent ideas; it merely introduces the infinitive verb that completes the meaning of be.
5. Common Sources of Confusion
5.1. Overlap with Prepositional “to”
Learners sometimes see sentences like:
- The decision is to be made tomorrow.
Here, to be looks similar to the prepositional to + noun pattern (to the office). Still, be is a verb, so the to is still an infinitive marker. The presence of the verb be after to is the key clue that we are dealing with an infinitive, not a preposition The details matter here..
5.2. Misidentifying Modal‑Like Constructions
Because be to can express obligation, it feels similar to modal verbs like must or should. This modal‑like quality can lead to the mistaken belief that to is functioning as a conjunction that links the subject to a modal idea. In reality, the modal meaning comes from the
