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fill=\"currentColor\" d=\"M14.234 10.162L22.977 0h-2.072l-7.591 8.824L7.251 0H.258l9.168 13.343L.258 24H2.33l8.016-9.318L16.749 24h6.993zm-2.837 3.299l-.929-1.329L3.076 1.56h3.182l5.965 8.532l.929 1.329l7.754 11.09h-3.182z\"\u002F>",{"id":47,"title":48,"author":49,"body":50,"cefrLevel":760,"date":49,"description":761,"exercises":762,"extension":820,"faqs":821,"gcseTier":49,"intro":49,"language":834,"lastUpdated":49,"meta":835,"navigation":836,"path":837,"seo":838,"stem":839,"verbSlugs":49,"__hash__":840},"pages\u002Fenglish\u002Fgrammar\u002Fmodals-of-deduction.md","Modals of deduction in English: must be, might be, could be and can't be",null,{"type":51,"value":52,"toc":748},"minimark",[53,70,79,84,87,183,194,211,215,220,239,257,273,277,291,308,329,358,362,365,423,436,451,455,474,491,505,524,528,603,607,610,698,702,705,739],[54,55,56,57,61,62,65,66,69],"p",{},"You look at the evidence in front of you and you say what you think is true.\nThe kitchen light is on, so somebody is home. The car is gone, so he has\nalready left. English does that job with modal verbs, and it is a different\njob from the one the same words do elsewhere. ",[58,59,60],"em",{},"Must"," here has nothing\nwhatever to do with obligation beyond the spelling. ",[58,63,64],{},"You must leave now"," is an\norder; ",[58,67,68],{},"she must be home"," is a guess. Same word, unrelated work. Once you\naccept that, the rest of the topic is a single scale from certain to\nimpossible, and a short list of forms to hang on it.",[54,71,72,73,78],{},"The ",[74,75,77],"a",{"href":76},"\u002Fenglish\u002Fgrammar\u002Fmodal-verbs","modal verbs"," page covers the whole family\nand the grammar rules they share. This page takes one of their jobs, guessing\nabout the present, and does it properly.",[80,81,83],"h2",{"id":82},"the-certainty-scale","The certainty scale",[54,85,86],{},"Every deduction you make sits somewhere between \"I am sure it is true\" and \"I\nam sure it is not true\". English marks the points on that line with different\nmodals.",[88,89,90,106],"table",{},[91,92,93],"thead",{},[94,95,96,100,103],"tr",{},[97,98,99],"th",{},"How sure you are",[97,101,102],{},"Form",[97,104,105],{},"Example",[107,108,109,125,140,154,168],"tbody",{},[94,110,111,115,120],{},[112,113,114],"td",{},"Sure it is true",[112,116,117],{},[58,118,119],{},"must be",[112,121,122],{},[58,123,124],{},"The lights are on. She must be home.",[94,126,127,130,135],{},[112,128,129],{},"Possible",[112,131,132],{},[58,133,134],{},"might be",[112,136,137],{},[58,138,139],{},"She might be at work.",[94,141,142,144,149],{},[112,143,129],{},[112,145,146],{},[58,147,148],{},"may be",[112,150,151],{},[58,152,153],{},"She may be at work.",[94,155,156,158,163],{},[112,157,129],{},[112,159,160],{},[58,161,162],{},"could be",[112,164,165],{},[58,166,167],{},"She could be at work.",[94,169,170,173,178],{},[112,171,172],{},"Sure it is not true",[112,174,175],{},[58,176,177],{},"can't be",[112,179,180],{},[58,181,182],{},"She can't be home, her car is gone.",[54,184,185,186,189,190,193],{},"Two things to notice straight away. First, the three middle forms mean\neffectively the same thing, so the real choice is only between three points,\nnot five. Second, the two ends are ",[58,187,188],{},"must"," and ",[58,191,192],{},"can't",", which do not look like\na pair. They are one anyway, and that is the whole difficulty of the topic.",[54,195,196,197,199,200,203,204,199,207,210],{},"Every form on that table uses the bare infinitive after the modal, exactly as\nthe modal rules require: ",[58,198,119],{},", not ",[58,201,202],{},"must to be","; ",[58,205,206],{},"might know",[58,208,209],{},"might\nknows",".",[80,212,214],{"id":213},"must-the-strongest-guess-and-not-an-order","must: the strongest guess, and not an order",[54,216,217,219],{},[58,218,60],{}," for deduction means you have worked something out and you are sure of\nthe answer. There is always evidence behind it, spoken or unspoken.",[221,222,223,229,234],"ul",{},[224,225,226],"li",{},[58,227,228],{},"Her coat is gone. She must be out.",[224,230,231],{},[58,232,233],{},"You have been walking since six. You must be tired.",[224,235,236],{},[58,237,238],{},"He has three houses. He must be rich.",[54,240,241,242,244,245,248,249,252,253,256],{},"Notice that ",[58,243,188],{}," is not the same as ",[58,246,247],{},"is",". If you knew, you would say ",[58,250,251],{},"she is\nout",". ",[58,254,255],{},"Must be"," says: I did not see it, but nothing else fits. It is a\nconclusion, not an observation.",[54,258,259,260,262,263,266,267,269,270,272],{},"The obligation use of ",[58,261,188],{}," (",[58,264,265],{},"you must wear a helmet",") shares the spelling and\nnothing else. You can tell them apart without thinking about it, because\nobligation ",[58,268,188],{}," points at a person and tells them to do something, while\ndeduction ",[58,271,188],{}," points at a fact and says it is true. If you can put \"I am\nsure\" in front of the sentence and it still makes sense, it is deduction.",[80,274,276],{"id":275},"cant-the-negative-and-the-mistake-everybody-makes","can't: the negative, and the mistake everybody makes",[54,278,279,280,284,285,288,289,210],{},"Here is the point of the whole page. When you are sure something is ",[281,282,283],"strong",{},"not","\ntrue, you do not use ",[58,286,287],{},"mustn't",". You use ",[281,290,192],{},[221,292,293,298,303],{},[224,294,295],{},[58,296,297],{},"He can't be forty. He looks twenty-five.",[224,299,300],{},[58,301,302],{},"That can't be her handwriting. She writes with her left hand.",[224,304,305],{},[58,306,307],{},"They can't be asleep. I can hear the radio.",[54,309,310,313,314,317,318,321,322,325,326,328],{},[58,311,312],{},"Mustn't"," means \"it is forbidden\". ",[58,315,316],{},"You mustn't be late"," is a rule about\nbehaviour. ",[58,319,320],{},"You can't be late"," (said while looking at a clock that says half\npast two) is a deduction about a fact. Learners reach for ",[58,323,324],{},"mustn't be"," because\nit looks like the tidy negative of ",[58,327,119],{},", and it is simply not what English\ndoes. Get this one thing right and you will sound noticeably more fluent than\nthe average B1 speaker.",[54,330,331,332,334,335,338,339,342,343,346,347,350,351,354,355,210],{},"The same asymmetry runs through the middle of the scale. The negative of\n",[58,333,134],{}," is ",[58,336,337],{},"might not be",", and that is fine: ",[58,340,341],{},"she might not be home"," says it\nis possible she is out. But there is no negative ",[58,344,345],{},"can be"," in this meaning. ",[58,348,349],{},"She\ncan be home"," does not work as a guess; use ",[58,352,353],{},"might"," or ",[58,356,357],{},"could",[80,359,361],{"id":360},"might-may-and-could-the-middle-ground","might, may and could: the middle ground",[54,363,364],{},"These three say the same thing: possible, and I am not committing. Choose on\nfeel rather than on rule.",[88,366,367,378],{},[91,368,369],{},[94,370,371,373,376],{},[97,372,102],{},[97,374,375],{},"Register and flavour",[97,377,105],{},[107,379,380,394,409],{},[94,381,382,386,389],{},[112,383,384],{},[58,385,353],{},[112,387,388],{},"the everyday default",[112,390,391],{},[58,392,393],{},"They might be stuck in traffic.",[94,395,396,401,404],{},[112,397,398],{},[58,399,400],{},"may",[112,402,403],{},"slightly more formal, more common in writing",[112,405,406],{},[58,407,408],{},"The delay may be due to the weather.",[94,410,411,415,418],{},[112,412,413],{},[58,414,357],{},[112,416,417],{},"one option out of several you are working through",[112,419,420],{},[58,421,422],{},"It could be the wind, or it could be the door.",[54,424,425,428,429,189,432,435],{},[58,426,427],{},"Could"," has a quiet second life here. ",[58,430,431],{},"It could be worse",[58,433,434],{},"that could be\nanyone"," are not really guesses about a specific fact; they open up a range. It\nis the modal you want when you are listing possibilities rather than picking\none.",[54,437,438,439,252,441,444,445,447,448,210],{},"Watch the negative with ",[58,440,357],{},[58,442,443],{},"She couldn't be at home"," means you are sure\nshe is not, which is the ",[58,446,192],{}," meaning, not the \"possible\" meaning. If you\nmean \"it is possible she is not at home\", say ",[58,449,450],{},"she might not be at home",[80,452,454],{"id":453},"deductions-about-what-is-happening-now","Deductions about what is happening now",[54,456,457,458,461,462,465,466,470,471,473],{},"To guess about an action in progress, put the modal in front of ",[58,459,460],{},"be"," plus the\n",[58,463,464],{},"-ing"," form. The modal supplies the certainty, the continuous supplies the now.\nThe ",[74,467,469],{"href":468},"\u002Fenglish\u002Fgrammar\u002Fpresent-continuous","present continuous"," page covers the\n",[58,472,464],{}," form itself.",[221,475,476,481,486],{},[224,477,478],{},[58,479,480],{},"She must be working late.",[224,482,483],{},[58,484,485],{},"They can't be sleeping, the light is on.",[224,487,488],{},[58,489,490],{},"He might be waiting outside.",[54,492,72,493,495,496,499,500,502,503,210],{},[58,494,460],{}," is not optional. ",[58,497,498],{},"She must working late"," is wrong; every one of these\nforms is modal + ",[58,501,460],{}," + ",[58,504,464],{},[54,506,507,508,511,512,515,516,519,520,210],{},"For deductions about the ",[281,509,510],{},"past",", English uses modal + ",[58,513,514],{},"have"," + past\nparticiple: ",[58,517,518],{},"she must have left, he can't have known, they might have missed\nthe train",". That is a big enough topic to have its own page: see\n",[74,521,523],{"href":522},"\u002Fenglish\u002Fgrammar\u002Fpast-modals","past modals",[80,525,527],{"id":526},"summary-table","Summary table",[88,529,530,546],{},[91,531,532],{},[94,533,534,537,540,543],{},[97,535,536],{},"Meaning",[97,538,539],{},"Present state",[97,541,542],{},"Present action",[97,544,545],{},"Past",[107,547,548,566,585],{},[94,549,550,552,556,561],{},[112,551,114],{},[112,553,554],{},[58,555,119],{},[112,557,558],{},[58,559,560],{},"must be working",[112,562,563],{},[58,564,565],{},"must have worked",[94,567,568,570,575,580],{},[112,569,129],{},[112,571,572],{},[58,573,574],{},"might \u002F may \u002F could be",[112,576,577],{},[58,578,579],{},"might be working",[112,581,582],{},[58,583,584],{},"might have worked",[94,586,587,589,593,598],{},[112,588,172],{},[112,590,591],{},[58,592,177],{},[112,594,595],{},[58,596,597],{},"can't be working",[112,599,600],{},[58,601,602],{},"can't have worked",[80,604,606],{"id":605},"common-mistakes","Common mistakes",[54,608,609],{},"Ranked by how often they actually turn up in learner writing.",[611,612,613,631,648,663,680],"ol",{},[224,614,615,620,621,624,625,252,628,630],{},[281,616,617,619],{},[58,618,324],{}," for the negative deduction."," ",[58,622,623],{},"He mustn't be at home"," should\nbe ",[58,626,627],{},"he can't be at home",[58,629,312],{}," is prohibition. This is the error to fix\nfirst, because it is the one native speakers notice.",[224,632,633,620,638,641,642,644,645,210],{},[281,634,635,636,210],{},"Dropping ",[58,637,460],{},[58,639,640],{},"She must working, they might sleeping."," The modal takes\nthe bare infinitive, and with a continuous meaning that infinitive is ",[58,643,460],{},":\n",[58,646,647],{},"she must be working",[224,649,650,620,656,659,660,662],{},[281,651,652,653,210],{},"Adding ",[58,654,655],{},"to",[58,657,658],{},"It must to be true, he might to know."," Core modals never\ntake ",[58,661,655],{},", in this use or any other.",[224,664,665,671,672,675,676,679],{},[281,666,667,668,670],{},"Using ",[58,669,188],{}," where English wants the present simple."," If you can see it\nwith your own eyes, do not deduce it. ",[58,673,674],{},"You must be Michael"," is right when you\nare guessing from a photograph; ",[58,677,678],{},"you are Michael"," is right when he has just\ntold you his name.",[224,681,682,620,687,690,691,693,694,354,696,210],{},[281,683,684,686],{},[58,685,345],{}," as a guess.",[58,688,689],{},"She can be at work"," does not mean \"she might be at\nwork\"; it means something closer to \"she is capable of being at work\", which\nis nonsense. Use ",[58,692,353],{},", ",[58,695,400],{},[58,697,357],{},[80,699,701],{"id":700},"practice","Practice",[54,703,704],{},"Choose the best modal. Answers are below.",[611,706,707,715,721,727,733],{},[224,708,709,710,714],{},"The office is dark, so it ",[711,712,713],"code",{},"___"," (must \u002F can't) be empty.",[224,716,717,718,720],{},"That ",[711,719,713],{}," (can't \u002F might) be John, he is in Spain this week.",[224,722,723,724,726],{},"I am not sure where my keys are. They ",[711,725,713],{}," (must \u002F could) be in the car.",[224,728,729,730,732],{},"She has read that book four times, so she ",[711,731,713],{}," (must \u002F might) like it.",[224,734,735,736,738],{},"They ",[711,737,713],{}," (mustn't \u002F can't) be out, I can hear the television.",[54,740,741,744,745,747],{},[281,742,743],{},"Answers:"," 1. must (the dark windows are the evidence) 2. can't (you are sure,\nbecause he is abroad) 3. could, or might (you are guessing between options) 4.\nmust (four readings is strong evidence) 5. can't (never ",[58,746,287],{}," for a negative\ndeduction).",{"title":749,"searchDepth":750,"depth":750,"links":751},"",2,[752,753,754,755,756,757,758,759],{"id":82,"depth":750,"text":83},{"id":213,"depth":750,"text":214},{"id":275,"depth":750,"text":276},{"id":360,"depth":750,"text":361},{"id":453,"depth":750,"text":454},{"id":526,"depth":750,"text":527},{"id":605,"depth":750,"text":606},{"id":700,"depth":750,"text":701},"B1-B2","How English guesses about the present with modal verbs: the certainty scale from must be to can't be, why the negative is can't and never mustn't, and the continuous form.",[763,784,804],{"type":764,"instructions":765,"options":766,"items":767},"which-one","Choose the modal that matches how sure the speaker is.",[188,353,192],[768,770,772,774,776,778,780,782],{"prompt":769,"answer":188},"The lights are on, so she ___ be home.",{"prompt":771,"answer":192},"He ___ be hungry, he has just eaten.",{"prompt":773,"answer":353},"I am not sure where they are. They ___ be at work.",{"prompt":775,"answer":192},"That ___ be her car, she does not drive.",{"prompt":777,"answer":188},"The door is open, so somebody ___ be inside.",{"prompt":779,"answer":353},"It ___ be true, but I want to hear it from him.",{"prompt":781,"answer":192},"He ___ be a doctor, he is still at school.",{"prompt":783,"answer":188},"She has been walking all day, so she ___ be tired.",{"type":785,"instructions":786,"items":787},"fill-blank","Write must, might or can't in each gap.",[788,790,792,794,796,798,800,802],{"prompt":789,"answer":188},"The shop is dark, so it ___ be closed.",{"prompt":791,"answer":353},"This ___ be the right road, but I am not sure.",{"prompt":793,"answer":192},"That ___ be Sam, he is in Spain this week.",{"prompt":795,"answer":188},"The cat is not in the house, so she ___ be in the garden.",{"prompt":797,"answer":353},"They ___ be at lunch, but I am not sure.",{"prompt":799,"answer":192},"He ___ know the answer, he has never read the book.",{"prompt":801,"answer":188},"Her coat is gone, so she ___ be out.",{"prompt":803,"answer":353},"Listen. Somebody ___ be playing music upstairs.",{"type":805,"instructions":806,"pairs":807},"match","Match each form to what the speaker means by it.",[808,810,812,814,816,818],{"left":119,"right":809},"I am sure it is true",{"left":177,"right":811},"I am sure it is not true",{"left":134,"right":813},"it is possible, I am not sure",{"left":148,"right":815},"it is possible, used more in writing",{"left":162,"right":817},"it is possible, one answer out of several",{"left":324,"right":819},"not a guess at all: it is not allowed","md",[822,825,828,831],{"q":823,"a":824},"What is the difference between must be and might be?","It is a difference of certainty, not of tense. Must be says you are sure: the lights are on, so she must be home. Might be says it is one possibility among several: she might be home, or she might be at work. Must be is the strongest guess you can make short of saying you know; might be, may be and could be all sit in the middle of the scale.",{"q":826,"a":827},"Why is can't be the negative of must be and not mustn't be?","Because mustn't is not a deduction at all. Mustn't means something is forbidden (you mustn't smoke here). When you are sure something is not true, English uses can't be: he can't be forty, he looks twenty-five. This is the single most common error in the topic. Must be and can't be are the pair; mustn't be belongs to a different conversation.",{"q":829,"a":830},"Is there any difference between might be, may be and could be?","Very little. All three say the thing is possible and you are not sure. May be is slightly more formal and turns up more in writing. Could be often suggests one option out of a set you are working through. In speech you can use whichever comes out first and nobody will hear a difference in meaning.",{"q":832,"a":833},"How do I make a deduction about something happening right now?","Put the modal in front of be plus the -ing form: she must be working late, they can't be sleeping, he might be waiting outside. The modal carries the certainty and the continuous form carries the now. Do not say she must working; the be cannot be dropped.","english",{},true,"\u002Fenglish\u002Fgrammar\u002Fmodals-of-deduction",{"title":48,"description":761},"english\u002Fgrammar\u002Fmodals-of-deduction","RPTLCQm3PE_-XP7t6yAX7TJP-zCsNEglxOuWPrhQ9Z4",{"left":4,"top":4,"width":5,"height":5,"rotate":4,"vFlip":6,"hFlip":6,"body":842},"\u003Cpath fill=\"none\" stroke=\"currentColor\" stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M13 21h8M15 5l4 4m2.174-2.188a1 1 0 0 0-3.986-3.987L3.842 16.174a2 2 0 0 0-.5.83l-1.321 4.352a.5.5 0 0 0 .623.622l4.353-1.32a2 2 0 0 0 .83-.497z\"\u002F>",{"left":4,"top":4,"width":5,"height":5,"rotate":4,"vFlip":6,"hFlip":6,"body":844},"\u003Cpath fill=\"none\" stroke=\"currentColor\" stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M11 4.702a.705.705 0 0 0-1.203-.498L6.413 7.587A1.4 1.4 0 0 1 5.416 8H3a1 1 0 0 0-1 1v6a1 1 0 0 0 1 1h2.416a1.4 1.4 0 0 1 .997.413l3.383 3.384A.705.705 0 0 0 11 19.298zM16 9a5 5 0 0 1 0 6m3.364 3.364a9 9 0 0 0 0-12.728\"\u002F>"]