What is the difference between a part of speech and a syntactic function / grammatical relation?

Question

What is the difference between a part-of-speech and a function? In other words:

1. What is a part of speech. (e.g. noun)

2. What is a grammatical function. (e.g. head, subject)

[read "grammatical relation" or possibly "syntactic role", if you prefer that terminology to "grammatical function" - see John Lawler's comments below]

3. What is the difference?

4. If we use a part of speech which is often used in one function, in a different function, does it change the part of speech of the word? For example, if we use a noun (let's say some nouny word that we can often observe functioning as a subject) as an adjunct, does it become an adverb?

Bounty Edit Note

These don't have to be addressed in different sections. One well illustrated paragraph which addresses the different concerns would be as welcome as a longer post with several parts!

I am hoping, though, that an answer to this question will, of course, give a description of what a grammatical function and part of speech actually are and not skip straight to the noun/adverb illustration!

I originally also asked about whether a noun used to modify another noun becomes an adjective as an example of a change of function. However, that has been covered in another question recently - though feel free to use it to illustrate your answer, if you'd like.

Motivation

Here's an example of why the question is interesting. In answers in rseponse to this question:

• What exactly is an "adverb"?

... several posts seem to indicate that a word's part of speech is determined by its function in a particular sentence. In other words, most answers on that page seem to argue that a part of speech is determined by how a particular word is being used. This is underlined in the top-voted and much linked-to answer:

... you will find that they have a category of adverb called a noun-adverb, meaning a noun used in a slot expecting an adverb, analogously to how a noun-adjective is a noun used in a slot expecting an adjective.

I wonder, however, whether functions and parts of speech can in fact be conflated in this way.

Answer 1

Parts of speech are categories, their members sharing various properties. One of these properties is the functions that the members can perform. These functions are relations, and each should be capable of coming before of. For example, in faculty office, faculty is a dependent (more specifically a modifier) of office. It generally makes no sense to say that something is a noun of or verb of.

If we look at families. Man and woman are categories (like parts of speech). You can see a man or woman outside of a family situation and generally still put them in the right category based on various properties such as facial hair, breasts, size, voice, etc. One of the properties of men is that they can function as 'husband of', 'brother of', 'parent of'. Women can be distinguished from men partly in their inability to function as 'husband of' or 'brother of', but both men and women can function as 'parent of'.

Back to words, the members of the category of English nouns share a range of properties including (typically) inflecting for number and ability to function as 'subject of' or 'object of' verbs. Adjectives have other properties, like inflecting for grade (tall, taller, tallest) and ability to function as 'modifier of' nouns. Number and gradability are distinguishing characteristics, but functioning as 'modifier of' nouns is a shared characteristic. But we can still distinguish them based on their other characteristics. Only when the word takes on many characteristics of another category (like fun--traditionally a noun--being inflected funner and funnest) would we say that it actually now belongs (also) to that new category.

Answer 2

For the time being, here is what Geoffrey Pullum has to say about this issue. This quote is taken from LEXICAL CATEGORIZATION IN ENGLISH DICTIONARIES AND TRADITIONAL GRAMMARS 2009:

Most of the deepest blunders in English grammar as traditionally presented over the past two or three centuries stem from a single long-standing confusion between (i) grammatical categories or word classes; (ii) syntactic functions or grammatical relations; and (iii) semantic and discourse-related notions.

It is surprising to see the tenacity of this confusion. It does not appear in other domains. People do not confuse butter knives with screwdrivers, even though occasionally someone who cannot find a screwdriver may use a butter knife to turn a screw. Yet in grammar people just cannot keep syntactically relevant categories or classes of words separate from the relational properties they have when used in particular constructions, and cannot keep either separate from meaning. They insist on trying to define the first of these in terms of the other two, and they have done so since the very earliest attempts to write grammars of English.

In short we need to be careful about confusing word categories and functions/grammatical relations. These two things are entirely different. A noun used as an adjunct or "adverbial" is still just a noun, not an adverb!

Answer 3

[Here is what I wrote in the comments before the question was re-opened.]

Okay here's my answer. In the understanding of a native speaker, each word has some potential meanings. Each meaning has both grammatical requirements and semantic requirements. Generally the working assumption in communication is that in a single instance exactly one of those meanings is in operation. If it is not possible to select one meaning for each word in a phrase such that all grammatical and semantic requirements are met, then it is recognized as invalid.

There are also rules, each of which allow words that have certain grammatical properties to function in other ways. Of course, for the speaker to know what rules apply, he already has to classify the meanings of each word, and even (unconsciously) weight them according to frequency in various contexts. That in turn is guided by the rules, in a self-reinforcing mechanism. The only criterion is simplicity. The more complicated a rule, the less likely it will be adopted or the more likely it will be forgotten or rejected by others.

Finally we can give a rough answer to the question, which is that the 'mental lexicon' we have tell us for each meaning whether it is a verb or noun or adjective or adverb or particle, and so on, not in the linguistic sense but in our own personal understanding. But that is just the 0th-order rules. The 1st-order rules then apply, allowing us to create on the fly new meanings based on their existing meanings, which are the 0th-order rules. In turn, there are 2nd-order rules, which allow us to create on the fly new 1st-order rules based on what kind of rules they are.

So as you realized in one of your comments, you can see that noun chains such as "noun chain reader strangulation problems." uses a whole string of nouns, all except the last as noun modifiers. It is not because each noun used has a 0th-order (lexical) meaning as a noun modifier, but because they have all been used as noun modifiers according to a 1st-order rule that essentially says that we can form noun chains where each noun will modify (via a suitable 0th-order meaning) the next noun in the chain. What problems? Strangulation problems. What strangulation? Reader strangulation...

Clearly there is subordination (consider "book problem" and "problem book"), so I would say that it's not helpful to say both are functioning as nouns despite what people may be used to saying. In my original comments I used "functioning as an adjective" instead of "functioning as a noun modifier", partly because ordinary native speakers just use the closest label they know for something that is modifying a noun. But I've changed it to make my terminology consistent. An adjective "A" is one that can be used in certain ways (which are described by 1st-order rules), such as to modify a noun, or having degrees of comparison via "more/less A" (not necessarily by morphology). A noun such as "book" and "problem", on the other hand, obey different 1st-order rules, such as not having degrees of comparison, and being able to modify nouns.

Lastly, I should say that we usually find a dictionary listing 0th-order rules and a grammar book listing higher order rules. So if you find two words listed as nouns in a dictionary, you can perhaps put them together to form a noun chain if their semantic meanings are compatible, in which case the first will function as a noun modifier. If it is not obvious how the meanings interact, you will create noun chain reader confusion. What you won't find is every noun in the dictionary listed as a noun modifier as well, unless it is not obvious how it is used as one, such as "noun phrase".

Answer 4

Parts of speech are word classes and word classes are different from parts of a sentence (or as you say "functions). And as they are different they should have different names. It's no good using "adjective" as word class and part of a sentence. In the same way "verb" is used as word class and sentence part. With such imprecise use of terms it is difficult to get a clear idea into the heads of learners of the way language works.

There are about eight or ten word classes and about five sentence parts, but it seems grammars are not able to convey these simple facts because they often use imprecise terms.

A noun can take the role of almost any sentence part except that of the verbal part. It can be subject, object, subject complement, object complement, it can be compound element of a noun (then often called adjective), it can occur in preposition groups which can be complements after to be or adverbial parts of a sentence.

Answer 5

Professor Lawler posted the following insightful and authoritative answer in non-searchable and ephemeral comments which I here reproduce verbatim as a Community Wiki answer to circumvent these infelicities:

Function is the wrong word; it’s pretty vague, even in linguistics. If you mean grammatical relation, however, that’s a term that refers to Subject, Direct Object, and Indirect Object; plus Oblique, which means “Everything Else”.

Parts of Speech (grammatical categories, not “functions” or relations) are syntactic (and occasionally morphological) categories that words can fall into. English has around 20 or so indispensable parts of speech, with lots of special-purpose cases. Most English words can fall into several categories. But there’s only 3 grammatical relations, plus Oblique.

And if you really do want to know what “grammatical function” means, you’ll hafta be specific about whose functional theory you’re referring to. I do use the word to refer to discernible affordances that certain structures offer, like the dozen or so syntactic rules (Extraposition, Right Dislocation, There-Insertion, etc.) that seem to have the function of moving heavy subject material to later in the sentence, to facilitate right-branching parse strategies.

But that’s not a technical term; there are all sorts of definition of “function” around, so you need some provenance.

Answer 6

I am assuming that your question uses "parts of speech" to mean much the same thing that my 9th grade English teacher used it to mean.  We can use words like "noun", "adjective", "preposition" and "gerund" to label different parts of speech.  I am assuming that you use "function" to mean something similar to what my teacher called "parts of the sentence".  Words that describe different parts of the sentence include "subject", "object", "complement" and "adjunct". 

The only way I can approach your question is to ignore my 9th grade English teacher -- that is, I need to avoid the terminology that she used.  If I understand your question correctly, I have to agree with you that "function" is a far better name than "part of the sentence".  In that spirit, I'll use "nature" as a better name than "part of speech".  We're looking at the difference between nature and function. 
 

It almost feels like Philosophy 101. 
 

If we're using the words "nature" and "function" as they are naturally used, then yes, there should be a difference between them.  Extending the Phil101 analogy, nature is a property of substance and function is a property of form.  For example, a tin bucket has the nature of tin and the functions of a bucket. 

We can make buckets out of other things.  Steel buckets work well, but so do wooden buckets and plastic buckets.  Paper buckets hardly work at all, unless they have a plastic or wax coating along their interiors. 

We can also make other things out of steel.  Steel makes a good conductor, and can easily form electrical wires and radio antennas.  We can't make everything out of steel.  For example, in its normal condition steel makes terrible seat cushions.  Oh, it can be done.  One way is to make steel springs. 
 

I'll try again. 
 

If we're using the words "nature" and "function" as this question requires, then yes, there should be a difference between them.  Extending apologies to my English teacher, nature is a property of a word and function is a property of a relationship.  For example, a noun subject has the nature of a noun and the function of a subject. 

We can make subjects out of other things.  Noun subjects work well, but so do clause subjects and infinitive subjects.  Adjective subjects hardly work at all, unless they have a clear antecedent in the manner of a pronoun. 

We can also make other things out of nouns.  A noun makes a good object, and can easily form direct objects and indirect objects.  We can't make all functions out of nouns.  For example, nouns make terrible predicators.  Oh, it can be done. One way is to use suffixes like -ize. 
 

Wash.  Rinse.  Repeat. 
 

The analogy seems sound to me.  Words have natures much like substances have natures.  We build structures out of words, and we craft things out of substances.  For a given purpose, a given word can be as well- or as ill-suited as any given substance would be for its intended purpose. 

I don't want to confuse the nature of a substance (such as a ceramic or a metal) with the structure of a thing (such as a teacup or a bucket).  I also don't want to confuse the nature of a word (such as a noun or an adjective) with the form of a function (such as a subject or an object).  There has to be a difference.  I'd never want to mistake all things ceramic for all teacup-like things.  I'd never want to mistake all nouns for all subject-like things.

Answer 7

These labels, 'part of speech' and 'function' plus their specific examples 'noun', 'verb', etc. and 'subject', 'object' etc., are tools to help us understand the (sometimes loose) rules of language (not just English). The labels help with getting the grammar right (whether as a school teacher/linguist or as a foreign language learner.

'Part of speech' (noun, verb, adjective, etc) tells you the broad category of a word, in general where and how it can be used in relation to others. Nowadays, the traditional Latinate 8 parts of speech have been reassessed for English and are much more refined (e.g. distinction between an article and a general adjective).

'Function' (subject/object, or participle/infinitive) tend to be restricted to a given part of speech. It tells you what grammatical markers might apply. For example, He and him are both pronouns, essentially the same thing, but the function, subject or object, tells you which one to use.

Another example, in 'he passed the ball' vs 'he wanted to pass the ball', the verb 'pass' appears in two different functions, 'passed' and 'to pass'.

Answer 8

What is a part of speech? What is a grammatical function?

Might as well ask: What's a noun? What's a verb? Why are they different?

This is the problem of the question. A noun is a person place or thing, and a verb is what a noun does or is.

Because a noun verbs, it doesn't stop being a noun as it verbs, so why should it stop being a noun as it adjectives?

Thus, why should a word defined as a specific part of speech by definition of what that part of speech is, change the part of speech because its function changes? The answer is: only if the definition of the noun is changed by changing the function.

What's a function? It's what a part of speech does.

You'll ask now, did I just verb the noun verb or did I use the noun verb erm. um... verbally?

Also, because it's not explicitly stated:
Where noun is used, part of speech can be reasonably interpreted to swap and the concepts hold. Where verb is used, grammatical function can be reasonably interpreted to swap and the concepts hold. Certainly not everywhere or else there will be an infinite loop and the Internet will implode.

Based upon comments: baptism is a noun. A ritual is a noun. It's a thing being done.

So, when I say a verb is what a noun does, I mean a noun runs, walks, baptizes, screams, answers, shrugs, writes, types and any other word that describes, per TheFreeDictionary:

any of a large class of words in a language that serve to indicate the occurrence or performance of an action, the existence of a state or condition, etc.

Because the question keeps moving: A verb is a part of speech that performs a grammatical function to indicate ... (the stuff quoted above).

Again the question moves:
OP in a comment that will be deleted soon enough:

So, according to that definition given by the free dictionary, (the kind of definition ridiculed by teachers and grammarians), arrival is a verb because it serve(s) to indicate the occurrence or performance of an action. You say that a verb performs a specific grammatical function, but you seem unwilling to give a simple definition of what a grammatical function is! I'm also confused because you seem to say that a noun is the doer of a particular verb. What about: The man was arrested. Is the man not a noun there?

Let's see. a function from the Free Dictionary is:

The action or purpose for which a person or thing is suited or employed Therefore, a grammatical function is the action or purpose for which a word is employed.

What are examples of grammatical functions? cited within About.com

"The production and interpretation of an utterance act is anchored to the constitutive parts of language: syntax, morphology, phonology, semantics and pragmatics. While syntax is composed of structural units, for instance constituents in traditional grammar, phrases in functional grammar and generative grammar, groups in systemic functional grammar or constructions in construction grammar, it is the linear ordering of the individual parts within a hierarchically structured sequence which constitutes their grammatical function. The adverb really, for instance, realizes the grammatical function of a sentence adverbial with wide scope if positioned initially or finally, as is the case in the utterance really, Sarah is sweet. If the adverb really is positioned medially, it is assigned the grammatical function of the adverbial of subjunct with narrow scope, as in Sarah is really sweet. Or, the proper noun Mary can realize the grammatical function of object in Sally kissed Mary, and it can realize the grammatical function of subject in Mary kissed Sally. Thus, it is not the grammatical construction as such which is assigned a grammatical function. Rather, it is the positioning of a grammatical construction within a hierarchically structured sequence which assigns it a grammatical function." (Anita Fetzer, "Contexts in Interaction: Relating Pragmatic Wastebaskets." What Is a Context?: Linguistic Approaches and Challenges, ed. by Rita Finkbeiner, Jörg Meibauer, and Petra B. Schumacher. John Benjamins, 2012)

Again from the OP in an ephemeral comment:

... or how about in They arrested the man? And regarding your concept verb: Are you saying that verb is a function? Or are you saying that verb is a part of speech? I'm confused.

I said a verb was a part of speech. It also performs a function. If you have to ask the question of whether a subject, direct object or an indirect object (all parts of speech called nouns) are in fact verbs because the action word (the part of speech called a verb) applies directly to the subject or one of the objects (nouns, whose grammatical function is a subject, direct object, or indirect object):

The man was arrested.

The: an article.
man: a noun. It's functioning as the subject. It doesn't change from being a noun because it's functioning as a subject. The definition of man does not change because of its grammatical function.
was arrested: a verb. It is functioning as the predicate. It doesn't change from being a verb because it has a function as a predicate. The definition of was arrested does not change because of its grammatical function.