I'm teaching ESL, and I came across a question from one of my students that I don't know how to answer. Using the form "{subject} {verb} {adjective} {infinitive phrase}" we've been going over sentences such as "I was happy to help you." (More specifically, "I helped you. I was happy. -> I was happy to help you.")

One of my students then suggested "I was tired to do my homework."

Now, as a native English speaker, I know that this is wrong. I'm even college educated and actually trained in ESL (which included grammar classes)... and yet, I have no idea WHY this is wrong. It SEEMS to fit the form our textbook was teaching ("I did my homework. I was tired." -> "I was tired to do my homework.") and yet I know it's wrong.

What's the difference? Why doesn't this work?

  • 17
    We are all tired to do your students' homework! Should probably be "of doing", but I'm tired. Dec 16, 2016 at 2:34
  • 35
    For approximately the same reason that "I was tired of doing my homework" works but "I was happy of doing my homework" doesn't. Dec 16, 2016 at 2:40
  • 11
    Don't come at it from a grammar angle; come at it from a semantic angle. "Happy/sad/reluctant to do X" denotes your attitude toward doing X before you start. You can't be "tired to do" something before you've started (although I suppose the thought of doing it can make you tired in advance). In other words, "tired to do" is a semantics issue, not a grammar issue. Also, it may work best to teach "sick/tired of x-ing" as idiomatic "chunks." (P.S. Welcome to EL&U!)
    – pyobum
    Dec 16, 2016 at 2:45
  • 30
    Interestingly, just adding a too makes it work: “I was too tired to do my homework.”
    – Jim
    Dec 16, 2016 at 2:52
  • 11

12 Answers 12


Let's change the main verb to "see". All the following adjectives accept an infinite

  1. I was happy to see her

  2. I was sorry to see her

  3. I was surprised to see her

  4. I was disappointed to see her

5a . I was sad to see her (go)

5b. I was saddened to see her

‘I was saddened to see their lack of commitment.’

  1. I was mad to see her

Incidentally, mad in British English usually means "crazy", so the speaker could be complaining:
“I must have been mad to see her, whatever was I thinking?”

  1. I was impatient to see her

  2. I was anxious to see her


  1. I was bored TO SEE her
    • I was bored of seeing her
    • I got bored seeing her

Similarly, it is equally ungrammatical to say: “I was bored to do my homework”
Google Books has innumerable results for bored to death, and bored to tears but none for was bored to do and only 4 instances for was bored to see And yet, bored is also a feeling or an emotion. A handy list of adjectives ending in -ed and -ing which may help the OP in his ESL lessons

  1. I was tired TO SEE her
    • I was tired of seeing her
    • I got tired seeing her

In sentence number 10, the speaker probably wanted to say they were too tired to meet someone, "too" often carries a negative meaning.

I was too tired to do my homework

As a result, I didn't do my homework.

However, using tired alone (without the adverb too) works as the reason for doing or not doing something.

  • He was tired to go to bed
  • He was tired, so he went to bed
  • We were tired to stop for a rest
  • We were tired, so we stopped for a rest
  • She was tired to see him
  • She was tired, so she didn't see him
  • I was tired to do my homework
  • I was tired, so I didn't do my homework

The same is true for the following synonyms of tired: weary, exhausted, sleepy, drained, burnt-out / burned-out.

I found an interesting older question on EL&U which mentions the usage of infinitives after adjectives. It doesn't specifically answer the OP's question but I consider it useful nevertheless.

To infinitive used after adjective.

The following is a short excerpt from @Araucaria's answer.

Adjectives which take infinitival phrases as complement fall into three camps.

  1. Some adjectives determine our interpretation of the subject of the infinitival clause.
  2. Some adjectives determine our interpretation of the object of the infinitival clause.
  3. Some adjectives don't determine our interpretation of either the subject or the object of the infinitival clause.

Group 3

Some adjectives don't fall into groups 1 or 2. We can't use them as predicate adjectives when they have an infinitival clause as complement. That is to say we can't use such adjective phrases as Predicative Complements. One of these adjectives is the word possible:

  • *A Rubik's cube is possible to be done.
  • *Pineapples are possible to grow here.
  • *Whales are possible to swim.

These sentences are ungrammatical. They are odd because they seem to be verging on the grammatical, but just don't seem to quite work properly.


Many users have repeatedly pointed out (see comments) that the adjective annoyed is used with the to-infinitive. The following pattern, ANNOYED AT + GERUND as in: I was annoyed at doing my homework, sounds far better to my ears; however, after searching a bit, I did find a few examples in the Oxford Learners' Dictionaries of annoyed + to-infinitive (to my consternation ☺).

  • 14
    "I was annoyed" does work. "I was annoyed to see her hit her brother" is admissible.
    – Andrew Leach
    Dec 16, 2016 at 8:09
  • 2
    "I am annoyed to do homework" simply doesn't work. But "I am annoyed at the idea of doing homework", " My having to do homework, annoys me" or "Doing homework annoys me" do.
    – Mari-Lou A
    Dec 16, 2016 at 8:39
  • 5
    re 6: "I was mad to see her" could also mean "I was desperate or excited to see her" as mad in British usage also means enthusiastic or excited. dictionary.cambridge.org/us/dictionary/english/mad
    – barbecue
    Dec 16, 2016 at 15:25
  • 15
    "I was annoyed to see her" makes perfect sense. E.g. "My aunt came over this weekend. I was annoyed to see her, because she always pesters me about getting married."
    – wjandrea
    Dec 16, 2016 at 20:08
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    @Mari-LouA I would say, "I was annoyed to do ...", but not "I was bored to do ...", because that would be "I was bored of doing ...". In my example, even if you separate the 'because' clause, it works just fine: "I was annoyed to see her. She always pesters me ...". I agree with other answerers that this a question of semantics, not grammar.
    – wjandrea
    Dec 16, 2016 at 20:22

If I had to guess, it would be that this form "{subject} {verb} {adjective} {infinitive phrase}" does not always work. The sentence you described, "I was happy to help you" will work but replace happy with other adjectives to see if it works.

I was hungry to help you

I was eager to help you

I was sad to help you

I was mad to help you

Out of all those sentences, the only one that actually made sense to me was "I was eager to help you", because it's just one of those common expressions. Similar to how "I was happy to help you" is a familiar phrase. But this doesn't mean that words such as sad and mad can not be used in the form "{subject} {verb} {adjective} {infinitive phrase}". For we can still say something such as

I was sad to hear that Craig Sager passed away today.

I was mad to see that question on the exam.

I was too tired to do my homework.

Like others have said, this most likely isn't a grammatical issue, rather, a semantics concept. It's related to why we wouldn't say "I am tired to eat right now" but why we would say "I am tired of eating cafeteria food".

EDIT: Seeing all the feedback on here has made me reconsider the validity of the sentence "I was tired to help you", so I hope I can congregate all the helpful feedback into my answer.

My four original examples

After reevaluating each sentence, I have to admit that each one was grammatically and logically correct.

I was hungry to help you

This can mean that I was desperate or extremely eager to help you.

I was sad to help you

This can mean that I was upset at the circumstances that lead you to needing my help.

I was mad to help you

This can mean that I really did not want to help you; therefore I was angry as a result for having to waste my time helping you.

Unfitting adjectives for certain indicative phrases

I agree with Mari-Lou A that adjectives such as possible are grammatically incorrect in the form "{subject} {verb} {adjective} {infinitive phrase}". The reason is that those kinds of words are usually structured with an infinitive phrase in this manner,

It is possible to grow onions there

It is unrealistic to assume that

It is imperative to hand your homework in on time

There are also adjectives that we can replace "tired" with that would not make sense either due to the lack of context or the lack of common meaning for the resultant phrase.

I was orange to help you

I was tall to help you

I was old to help you

What does it mean to be orange, tall, and old in these cases? Compare these sentences with

I was crazy to help you

I was foolish to help you

I believe that these sentences are all grammatically correct, but we only associate meanings with particular phrases. It may be possible that "I was tired to help you" and even the three sentences above all have legitimate meanings. However, I am not familiar with them because I have not heard these phrases used often.

The addition of too

An interesting point is that if you add too before tired, then the sentence seems to make more sense.

I was too tired to help you

Now in this case, being "too tired" has some common meaning associated to it. It means that I could not help you because I was tired at the time you required my assistance. We can add this word to our previous sentences to completely change their meaning

I was too hungry to help you

I was too upset to help you

I was too frustrated to help you

All these sentences have a common thread, which is the fact they all have the connotation that the action indicated in the infinitive phrase was never completed. So could it be that words such as tired can only express an incompleted action and that is why it requires the addition of too? I'm afraid this hypothesis has no validity, for some of Mari-Lou A's valid sentences included

I was anxious to meet her

I was impatient to meet her

Both these sentences do not guarantee that the action in the infinitive phrase actually occurred.

adjective + preposition + gerund

Another interesting point was how adjectives that work with the form "{adjective}{proposition}{gerund}" may not abide by the form "{subject} {verb} {adjective} {infinitive phrase}". The word tired falls into this category because of these two statements

I was tired to help you

I was tired of helping you

The second sentence means that I don't want to continue helping you. Other words such as afraid and bored fall into this category

I was afraid to help you

I was bored to help you

I was afraid of helping you

I was bored of helping you

It is a legitimate argument to claim that the first example, "I was afraid to help you" is completely valid. Unfortunately the second example, "I was bored to help you" falls into the category of less familiar sentences such as "I was tired to help you". So the gerund topic did not get us very far.

My final thoughts

What does it mean "to be tired to help someone"? Can we replace tired with a synonym to get a similar sounding sentence that is more commonplace? Exhausted, weary, and fatigued don't seem to work either, or do they? Looking at the sentence, "I was happy to help you", I tried to decipher what it meant. It simply means that I wanted to help you because it gave me satisfaction. Could it be possible that "I was tired to help you" has a meaning that we are not fully aware of? I only asked this because users were arguing about the meaning of phrases with questionable adjectives like "I was annoyed to see her" and "I was mad to see her". It may very well have to do with why "I was not there to help you" works but "I was absent to help you" doesn't. All of the examples could be grammatically correct but we don't know what they all indicate.

  • 2
    I think that's questionable, because even in those other "to help you" examples you gave, I see them as perfectly grammatical. Maybe the situations that would elicit such sentences are a little uncommon, but there's nothing wrong with the structure. "I was sad to help you" for instance... maybe you were recently injured making you need help, which makes me sad. Or maybe you aren't putting in the proper effort I think you're capable of, which makes me sad. It still works as a sentence, even if maybe uncommon. Similarly with the others. Dec 16, 2016 at 3:55
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    The phrase 'I was mad to help you' does work as an exclamation, i.e. 'I was mad to help you!' with the meaning 'It was crazy of me to have helped you'. Dec 16, 2016 at 8:19
  • 5
    Sorry, all four of the initial examples here are perfectly fine. Dec 16, 2016 at 10:32
  • 2
    I agree most of these examples are perfectly reasonable. Better examples of inappropriate adjectives would be tall, or orange, or spidery.
    – barbecue
    Dec 16, 2016 at 15:32
  • 3
    +1 for the comprehensive edit. Also, given the current Western political climate, I'm now desperate to hear a certain incoming leader say “I am too orange to help you”. Dec 16, 2016 at 23:25

I’m afraid the answer is ultimately a very disappointing “because it is”.

There are various types of adjectives, and like verbs, different adjectives have different properties of valency. Some cannot take any complements; some can take one or more optional complements; and some must take one or more mandatory complements. Of those that can or must take complements, some license infinitival complements, some license gerund/participial complements, some license prepositional complements, and some license any combination of these complement types. (Some even license noun-phrase complements, but they’re few and not relevant here.)

The answer by Araucaria that Mari-Lou dug up and linked to in her answer does a good job of describing the underlying properties that govern how the subgrouping of infinitival complement-licensing adjectives determines which constructions they may be used in. But in the same way that there is no way of knowing, a priori, whether a given verb is intransitive, transitive, or ditransitive—or indeed whether it licenses any other kind of complement—there is no way of knowing what group an adjective belongs to to begin with.

Even within the group of adjectives that license infinitival complements, there are many variations. For example, although happy and angry are both adjectives that describe emotional states and can take infinitival complements, the type of verb they allow in that complement differs. With evidential verbs like see/hear/find/notice, both work just fine:

I was happy to find that they’d left already.
I was angry to find that they’d left already.

But with what we might call ‘simple action verbs’, they are unequal:

I has happy to do my homework.
†I was angry to do my homework.

With participial complements, on the other hand, they converge again:

I was happy seeing that they’d left already.
I was happy doing my homework.
I was angry seeing that they’d left already.
I was angry doing my homework.

They also both license prepositional complements:

I was happy at finding that they’d left already.
I was happy from doing my homework.
I was angry at finding that they’d left already.
I was angry from doing my homework.

Doing the same thing with tired, it is clear that this adjective is perfectly happy (!) to license prepositional and participial complements:

I was tired from working.
I was tired at the prospect of working.
I was tired of working.
I was tired working at the wheel all day.
(?)I was tired working.

But there is just no infinitival complement that is allowed:

†I was tired to see that they’d left already.
†I was tired to do my homework.
†It is tired to be a good worker.
†I am tired for him to work.


So we can conclude that happy, angry, and tired all license participial complements and various types of prepositional complements; but where tired doesn’t license infinitival complements at all, angry licenses evidential ones, and happy seemingly licenses just about any type imaginable (at least I can’t think of one that won’t work).

What we can’t conclude anything about is why this is so. That is simply a property that has to be learnt individually for every adjective, just like transitivity and phrasal verb constructions must be learnt individually for each verb.

  • 3
    @Wildcard Terminology is nothing but a convenient way of describing complex semantic notions in relatively few words, to make sure everyone is on the same page and knows what’s being discussed. The terminology itself doesn’t really matter (as long as it’s understood), and there isn’t really any emphasis on it in my answer here. It’s the notions behind it that matter. I don’t understand where you’re getting a prescriptivist vibe from, though—there is no prescriptivism in stating that you just have to learn what constructions each adjective can and cannot be used in. That’s just fact. Dec 18, 2016 at 11:00
  • +1 Nice post. Are the gerund-participle clauses complements though? Or are they adjuncts? Seeing that they'd left already, I was happy etc. Aug 6, 2017 at 0:15
  • @Araucaria Hm, good point. They may be, though at least with happy, there's a difference to me between the complement-like usage and the adjunct (or sentence-adverbial) usage: “I was happy being a carpenter” is a statement about me; “Being a carpenter, I was happy” is a statement about carpenters. I think they're at least arguably complements. Aug 6, 2017 at 5:44

When to-infinitive is used adverbially, it implies (1) purpose, (2) cause (rasson) of feeling or emotion, (3) result (of an action), etc.

There are adjectives that describe people's feeling and emotions that are followed by to-infinitive. For example, let's change the sentence in the question to

I was happy to finish my homework.

This sentence implies.

(1) Finishing my homework is the cause of my feeling happiness.

(2) Without finishing my homework, I would not have felt happy.

(3) Finishing my homework was done only once (one-time, non-repetitive action). To infinitive usually doesn't imply repetitive actions.

(Note @Bolben's comment: It can also mean I was perfectly willing to finish my homework. In this case, to-infinitive is closer to purpose than cause)

However, "I was tired to do my homework" is not idiomatic because

(1) Tired is not related with feeling or emotion. It only means physical fatigue created as a result of some continuous or repetitive actions.

(2) In order to feel tired, you need to do something continuously or repetitively. Gerund or -ing form is more suitable for continuous or repetitive action than to infinitive.

The reason "I was too tired to do my homework." works is the to-infinitive indicates purpose (or result). In other words, the sentence means "In order to do my homework I was too tired and that's why I couldn't do it" or "I was very tired and as a result I couldn't do my homework."

Other adjectives that can be followed by to-infinitive are afraid, ashamed, glad, pleased, proud, sad, sorry, etc. Compare the following two sentences:

(1) I was afraid to jump.

(2) I was afraid of jumping.

No. (1) indicates jumping is the cause of my feeling fear or anxiety at a specific point of time in the past. No. (2) indicates I generally felt fear or anxiety about jumping.

What's the difference? Why doesn't this work?

There are differences between to-infinitive and -ing form in terms of their function and usages. When there are adjectives describing people's emotion or feeling, using to-infinitive is more idiomatic to indicate their cause (or purpose).

  • 1
    There is an alternative implication of I was happy to finish my homework which you have not mentioned. It can also mean I was perfectly willing to finish my homework. There are many possible reasons for this which would be made clear by other parts of the same passage. For example I was happy to finish my homework before I went out or My girlfriend arrived while I was doing my homework. I was happy to finish my homework after she left. In neither of these cases is there the implication that the completion of the homework was the cause of a feeling of happiness.
    – BoldBen
    Dec 17, 2016 at 8:06
  • @BoldBen Thanks for the comment. That's the point ArtOfCode raised in the comments to the question. Yes, it's possible and it is closer to "purpose" than "cause". That's what to-infinitive is for. It will take a doctoral dissertation to answer this question if you want to include every possible meaning and connotation.
    – user140086
    Dec 17, 2016 at 8:10
  • Absolutely, this question could run and run!
    – BoldBen
    Dec 17, 2016 at 8:14
  • @BoldBen I've edited my answer a little. Please take a look.
    – user140086
    Dec 17, 2016 at 8:14
  • The jump versus jumping comparison is very helpful +1. The above answers don't really answer the question; I'm not sure why they're so highly voted. Dec 19, 2016 at 0:19

It doesn't work because "I was tired to" is not an idiom. Like an idiom it's ungrammatical, but that's as far as the parallel gets.

"I was happy to (do my homework/see her/find $10 in the street)" is an idiom. The grammatical way to express the same idea is "I felt happy when I (did my homework/saw her/found a tenner in the street)"

"I felt tired when I (did my homework/saw her/found a tenner in the street)" is also grammatical, if not in the case of the tenner very sensible. But you can't back-patch to get the idiom because an idiom doesn't exist for "tired to" the way it does for "happy to".

  • 1
    Idioms are arguably never ungrammatical, but are either extragrammatical (not using normal grammar), use words in unusual senses, or both. Dec 16, 2016 at 15:30
  • I'd probably argue that "extragrammatical" is a type of ungrammaticality, since if it lies outside normative grammar it's therefore not grammatical, thus ungrammatical, but I probably wouldn't put too much energy into it :-)
    – MMacD
    Dec 16, 2016 at 17:08
  • 'Ungrammatical' and 'unacceptable' are nigh on hyponym and hypernym. I used the term my favourite work on idioms / fixed expressions (by Moon) uses. Dec 16, 2016 at 17:10
  • Now there's a pair of words y'don't hear very often! I think you are probably the first person ever to use them in my presence (fsvo presence).
    – MMacD
    Dec 16, 2016 at 17:15

There are some adjectives that can be used with an infinitive, and some that cannot. (Tired is an adjective that cannot be used with an infinitive.)

I started to agree with MMacD in saying that "happy to" is idiomatic. "I was happy to do my homework" doesn't mean that doing homework made me happy, or even that I truly was happy while doing my homework. Instead, "happy to" is an idiom for "willing to", "pleased to", and so on.

Upon further reflection, I am not sure that this is strictly an idiom. Regardless, the infinitive phrase changes the meaning of "happy".

It is interesting how inserting "too" changes things:

I was happy to do my homework.

...Happy works with the infinitive to form a phrase conveying willingness.

I was too happy to do my homework.

...Happy is a regular adjective that modifies the subject, and implies that I did NOT do my homework because of my condition of happiness.

Ain't English grand.


I was happy to help you is equivalent to I was happy that I helped / could help you. In other words, happy is an adjective that in its predicative use may take a complement with the form of a content clause (Cambridge Grammar of the English Language, p964).

Among the other "adjectives that license declarative content clauses as complement" that the CGEL lists are: eager, glad, annoyed, pleased, proud, upset.

Tired is not in the CGEL's list, and the utterance I was tired that I did / could do my homework is ungrammatical - as is the equivalent I was tired to do my homework. Furthermore, it is semantically problematic.

I think the OP's textbook illustrates the danger of transformation exercises that pay no regard to the meaning of the resulting conversion.


I am not a native English speaker, hence maybe I could help adding comments from a different angle. The key of the idiom using the gerund after adjectives like "tired" could be the fact that, as English uses the verb "to be" either for "to have presence in the realm of perceived reality; exist; live" or "to take place; occur"(Collins Dictionary), the language needs to remark the difference of being a perception of the reality plus a self existed presence and, on the other hand, being an occurrence. In the sentence "I am happy" the subject is meaning that he/she perceived happiness. In the sentence "I am tired" the subject is denoting an occurrence. Latin languages, like Spanish, have different verbs: "ser" or "estar" to express one or another meaning. At the same level, in Spanish is not correct to use "ser" with some adjectives and the same instance for "estar", though it is possible to use any of them with the same adjective which, however, gives different meaning to the sentence (English translation of ser (Collins Dictionary) and English translation of estar (Collins Dictionary)).

Yet in Spanish is not correct saying: "soy cansado", or in the past "fui cansado" which means that my being or my existance is tired, but it must be said "estoy cansado" or "estuve/estaba cansado" which means that a certain activity is affecting me for a short period of time. With "happy" we can say "soy/fui feliz" if we mean that my happiness is durable and "exists" within my being, and also we can express "estoy/estuve feliz" if my happiness is/was owed to a particular or certain happening or occurrence in an accountable period of time. This is working in the same way with other adjectives like boring, sick, angry, hungry, sad, etc.

I am not sure if this is a very philological explanation, however, at least for a foreign student, it could shed some light on the use of gerund or infinitive after some adjectives in English.


I think part of the reason the second sentence (tired to do my homework) doesn't work is that it can mean more than one thing - offhand, I've thought of three - and there isn't enough information. So it comes across as incoherent, or incomplete. When using "I was happy to", there is really only one way of translating it - that the action was done, and the person claimed to be happy about it. Happy is positive, and simple to understand in context. But tired, especially in the context of more effort, is negative - but maybe and maybe not the negative of the action, or negative of the reaction, or just a downside.

I was tired to do my homework.

It could mean I did my homework, and I was tired. It could mean, I did not do my homework, because I was tired. It could mean, I am tired of doing my homework.

If you did your homework, but was tired (direct comparison to the "happy to" construction) then...why is it one sentence? If you were tired as a result of doing homework, there's no reason to have it first in the sentence and it is a bit unusual ("I was tired and did my homework", and "I did my homework and was tired", actually mean different things), and if the two weren't related, it makes little sense to keep them in the same question - it reads as disjointed.

If you did not do your homework, because you were tired - you sort of need to signal that negation, and you don't. If you said, "I was too tired" the "too" serves as that signal, "too much" means something didn't work because the quantities are off. Alternatively, you have to say something about relation or sequence to make the combination make sense.

If you are tired of doing your homework, you have made no statement about whether the homework is done or not. Very neutral. You have just signaled a state of mind, or your reaction to homework or its being-done-ness - this feels like the closest analogy to the use of "happy", actually, since it's separate information and effects the work coming and going - but you still need to signal that the other interpretations aren't what you meant.

In any case, since you kind of don't signal what the relation is between the two parts of the sentence ("I was -" and "to do my -"), your listener has to fill in the blanks with how the two are connected. Happy really only means one thing, no matter which causes which (happy because homework, happy while homework, homework while happy, it's all good). So it's easy, in that case, to figure out what the person meant. Tired can mean a couple things, depending on what the tired was doing to the homework, or the homework doing to the tired. So we need a bit more info to figure out what's going on - and without that info, the sentence doesn't parse.

  • 1
    +1 I wouldn't have put it quite the same way, but this is close enough to what I would have said that it saves me the trouble of duplicating it. Thanks, @Megha. Executive summary: there are a lot of different kinds of predicate adjectives and they behave differently with subordinate clauses. Especially when the adjectives describe human mental or emotional states, which are already vague to start with. Dec 17, 2016 at 18:59

The segment "...was tired to do..." conflicts past/present/future tenses.

I was happy to do my home work

Happy has no tense, or rather it has a variable tense; to do is either present or future tense. The interesting part of the sentence can be grammatically simplified to:

Happy to do it

Consider the simplification substituting past tense "tired" for no tense "happy":

Tired to do it

...it doesn't work, since "tired" is past tense.(1)

I can't think of a Modern English tenseless drop-in equivalent for "tired", but there is the archaic "aweary" which provides the correct tense and sense of it, albeit obscurely:

I was aweary to do my homework.

(Note that plain "weary" also won't work.)


    1. Like tired, some adjectives ending in "-ed" don't work there, (e.g. bored, numbed, bombed, etc.), and yet some do, (e.g. prepared, stoked, thrilled, etc.). Why the latter set works would be a separate question.
  • You've said the past tense is the reason for it not working, then gone on to list an example of the past tense working, claiming it is a separate question. This doesn't seem logically consistent to me
    – binaryfunt
    Jan 26, 2018 at 14:29
  • @binaryfunt, Re "doesn't seem logically consistent": that raises a more general question of "are any natural language's grammars logically consistent"? English in particular is a bit of a mash-up, so even if those languages that contributed to it were consistent, perhaps certain combinations aren't, which grinds their collective gears. Perhaps English grammar is inconsistent similar to how its orthography is.
    – agc
    Jan 26, 2018 at 15:49

More specifically, "I helped you. I was happy. -> I was happy to help you."

I think the root of the issue is that this is a overly simplistic way to think about how the sentence is constructed. You provided a poor rule, and the student tried to apply it to a different situation, where it failed.

One way it fails is that it glosses over the relationship (if any) between being happy and helping.

It is not merely that I happened to be happy while I was helping you, it is that I was happy that I was able to help you. I want you to succeed, and I was happy to be that person that was able to help you when you needed it.

And in this case "happy to help you" works not because of your rule, but because the phrase "happy to (do something)" means something more than just the conjunction of its words. Not sure if "idiomatic" is the right way to describe it, other answers probably give it a better label.

"I was tired to do my homework."

So the "rule" fails here. Part of the problem is that "tired to (do something) isn't an idiomatic phrase like "happy to (do something)" is.

But more than that, what exactly is the connection between "tired" and "homework" that the student is trying to convey?

Were you too tired to do your homework (so you didn't do it)?

Did you just feel tired while you were doing your homework, but you soldiered through?

Did you complete it, but the quality of your homework suffered because you were tired?

All of these would be constructed differently, perhaps something like:

  • "I was too tired to do my homework, so I went to sleep."
  • "I was so tired doing my homework last night, but I got it done."
  • "I was so tired doing my homework, I hope the professor is just as tired grading it."
  • But you're ignoring the fact that the formula, or rule —which many English course books recite— works for a great many other adjectives: "I was delighted/disappointed/thrilled/mad/sad/scared (etc.) to help her." These are all perfectly grammatical, and make semantic sense. Although "I was thrilled to help her" is not a typical idiom, it still makes prefect sense. There would be no "rule" to speak of, if it only worked with the adjective "happy". You could call "tired" an exception to the rule.
    – Mari-Lou A
    Dec 19, 2016 at 17:48
  • @Mari-LouA Ok, I accept your point. But then doesn't that restrict us to just adjectives that are emotions (delighted/happy/disappointed, etc)? You wouldn't say someone is "polite to help you" or "tanned to help you" or "strong to help you" or "wet to help you", even if they just came in out of the rain... errr, actually I'd probably skip that last one for new English learners not familiar with euphemism.... Anyway, "bored" and "tired" are probably somewhere in the middle, but for this purpose they fall into the later category, not the former.
    – BradC
    Dec 19, 2016 at 19:05

I'm going to have to answer, because it appears I'm the only person who thinks it's a valid, but obscure response:

"Your homework is so good today James!" said Miss Barrass.

"I was happy to do my homework Miss. I think that's why it is so good." he replied.


"Your homework is not so good today James!" said Miss Barrass.

"I was tired to do my homework Miss. I think that's why it is not so good." he replied.

It's almost certainly my perception, given all of the other answers, however the more I read this, the more I feel it's acceptable and perfectly valid. It's just not in common usage, which makes it sound strange.


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