The side effects can and have occurred.

The omitted verb is an infinitive (occur) but the written verb is a past participle (occurred).

Is this sentence grammatically correct and suitable for formal writing?

If so, what are the rules for omitting verbs? Also, is it possible to make a question using the same pattern? For example, "Can and have the side effects occurred?"

  • 1
    There is no omitted verb in the present tense: occur is the infinitive as befits a verb modified by a modal can.
    – tchrist
    Oct 27, 2014 at 4:44
  • Great! That information is very useful. Thank you! Oct 27, 2014 at 5:18
  • Do you think this is a suitable explanation (I need to explain this to an non-native speaker)? Can must be followed by an infinitive verb so the reader will automatically assume the meaning of the sentence, The________ can and have occurred= The ______ can occur(infinitive) and have occurred. Oct 27, 2014 at 6:18
  • 'tchrist. occur is indeed the infinitive, but it's not there. This infinitive has been (incorrectly) omitted.
    – tunny
    Oct 27, 2014 at 7:15
  • In addition to what tchrist says, "have occurred" is present perfect, not past perfect. Past perfect would be "had occurred".
    – RegDwigнt
    Nov 26, 2014 at 10:58

2 Answers 2


"The side effects can and did occur." is correct, but "The side effects can and have occurred." is not.

In the first example the omitted word (occur) is the same, because the tense of the contracted verb agrees agrees with the remaining verb. i.e. both are in the simple tense, so can (simple future) and did (simple past) both take the conjugation "occur".

Using "have" introduces the perfect tense and therefore "occur" would become "occurred" in its expanded form, so the sentence originally would have read:

"The side effects can and have occurred.", when written in full would read "The side effects can occurred and have occurred." This is obviously incorrect.

A contraction like this is used for the reader's (and writer's) convenience. In order to be grammatically acceptable, the contracted sentence must still make sense in its expanded (original) form.

  • In order to be grammatically acceptable, "a contraction like this is used" is perfectly sufficient. Grammar is not about inconvenience, convenience is not ungrammatical, and a sentence does not have to make any sense at all to be grammatically correct. Also, perfect is an aspect, not a tense.
    – RegDwigнt
    Nov 26, 2014 at 12:00

The reality of the language is such that this kind of ellipsis is not unheard of, and is indeed rather common. The Corpus of Contemporary American English has 27 cites for "can and have", and the British National Corpus has 8.

Out of these 35 cites in total, at least 10 are actually from academic publications, which is an unusually high proportion, and more still are from newspapers, magazines, or books. Here are a few for your convenience:

  • Reform plans can and have been constrained (if not defeated) particularly in the foreign policy arena by the preferences of the supreme leader.
    Journal of International Affairs, 2003

  • From a constructionist perspective, however, individuals and entire groups can and have shifted from one category to another, from non-white to white and even on occasion from white to non-white.
    Journal of American Ethnic History, 1999

  • Although federal troops can and have been used to assist local authorities in emergencies when requested by state officials, they are not authorized to enforce local laws.
    ABA Journal, 1999

  • Accidents can and have been defined in terms of the statistics collected by the DTI (see above), and most of these clearly involve an interaction between the individual and the environment.
    Current Psychology, 1996

  • They also can and have been used as rationales for maintaining the status quo of our healthcare system.
    Hospital Topics, 1993

  • The company secretarial department of the firm can and have acted in this role on occasions.
    KPMG MAS engagement manual, 1993

  • There are two broad approaches to inadequacy that can and have been taken.
    Public finance and public choice, 1992

  • Universities can and have contributed to Geological Survey research[.]
    Misc unpublished — The purpose and use of the research, undated

  • Liberation theologians can and have replied, "Don't ask us; we are theologians, not economists or political scientists."
    Theological Studies, 1992

  • They can and have safeguarded the provision of humanitarian aid.
    Liverpool Daily Post and Echo, undated

  • Low-end PC makers can and have shrugged off the three-month delay imposed on the P5.
    Unigram x, undated

  • The character of social classes and class structure, the problems of ideologies and cultural traditions, the emergence of a relatively autonomous state and of the systemic qualities of world economic interactions can and have been informed by Marxist intellectual traditions.
    Social Research, 1990

  • Components can and have been handled where the drawing reference and attitude bear no relationship to the kinematic motion.
    The computer-based design process, 1986

Do note the vast variety of fields: history, politics, theology, psychology, medicine, sociology, mechanical engineering, finance.

Now, 35 cites is not much — the corpora have over 1 million cites for can alone, and over 2 million for have —, but it's enough to show that this is not a one-off error, nor a construction limited to careless speech. And to further put the number into perspective, the corpora have only 12 cites for "orange car", and only 7 for "cool beer".

All that said, you are of course still free to omit this kind of ellipsis. And we are free to call it strange, clumsy, or illogical. We just can't call it ungrammatical. Grammatical constructions are under no obligation to be logical, unclumsy, or unstrange.

I won't leave you without a caveat, though: all of the above only holds for can specifically. The corpora barely have a single cite for this construction with any other modal.

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