I am preparing a seminar talk. Currently the presentation contains some theorems and some proofs. Probably, I will not have time to explain all the proofs - I will have to skip some of them. My question is, which of the two options is better:

  1. Keep the slides with the proofs visible, and during the presentation, if I see that the time is tight, rush through them saying that "I skip the proof", or -

  2. Keep the slides with the proofs hidden, and during the presentation, if I see that there is enough time, unhide and go through them?

The advantage of option 1 is that the audience sees that I have a proof and they can read it later if they want; also, if I have time it is easier to present the proof; the disadvantage is that it might look confusing or unprofessional to rush through slides. Are there other considerations?

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    Yes: it will look unprofessional to rush through slides. Rule of thumb: The talk always takes longer than you think it will. Halmos' advice: a mathematics talk should contain at most one proof. – GEdgar Sep 17 at 12:26
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    This is not an answer to your question, so I put it as comment: slides.com, and I'm guessing some slides creating application, allow you to organise your slides in two dimensions, which then allows you to skip slides without anyone noticing. – Nico Sep 17 at 14:30
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    I wouldn't call it unprofessional (unless you are constantly flipping around and make yourself look like a lost and unprepared mess) but it generally is disorienting to show slides you don't explain, and hence is advised against. But what is more important to you, maximizing audience comfort in and retention of material, or impressing them with your research achievements? – A Simple Algorithm Sep 17 at 17:03
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    Personally, I hate it when the speaker has one thing on the slide but speaks about another one. My attention tends to switch between the two and I might end up not understanding either one. If you are not planning to explain the proof, then don't show it on the slide. – Szabolcs Sep 17 at 18:07
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    "if there is enough time" for proofs?!? You should practice your presentation so that you time it close to the time allotted. Thus you should know how long your presentation will take. There is usually a defined time for Q&A's after the presentation. – MaxW Sep 17 at 21:36

10 Answers 10

Put the slides that contain the proofs after the last slide and have links on the relevant slides so you can jump to the proof slide and back to the next one.

That way no-one will know if you skip the proofs, but they could see you click the link to jump to a proof if you have the time.

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    That also works well if there is insufficient time during the presentation, but you get asked about the proof during questions. – Patricia Shanahan Sep 17 at 11:57
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    Yes, always good to have the extra slides ready after your closing one - proofs, other references etc etc – Solar Mike Sep 17 at 11:59
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    Zongker, D. demonstrates this invaluable technique. – Kevin Sep 18 at 2:20
  • @PatriciaShanahan As illustrated at 3:38 of this famous talk. – David Schwartz Sep 19 at 18:09
  • @Kevin came here for exactly that comment – De Novo Sep 20 at 0:09

I use a 2D layout for that.

I do not know the software you will be using, with reveal.js you can have a linear progression, and some slides can go "down" (these are the detailed ones).

This way I get to keep the continuity of the presentation, and move deeper if needed.

  • I guess LaTeX/Beamer offers something similar. – user2768 Sep 19 at 6:48
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    @user2768: I've also seen it in other software (prezi I think) and it is a shame that PowerPoint and Google Slide all follow a linear structure, instead of having a multi-level one (2 directions is good, having a whole tree would be better) – WoJ Sep 19 at 6:56
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    @user2768 If it does, I have never seen it. You can put clickable links from one page to another one (for instance, Beamer shows some navigation symbols by default), but not have more than two navigation keys, as far as I know. And I guess it's a feature that would require some support from the pdf reader to work. – Federico Poloni Sep 19 at 18:10
  • @FedericoPoloni Overlays will get you started. – user2768 Sep 20 at 7:20

While I love the answer from Solar Mike and the comment from GEdgar, I'd like to offer an alternative that has sometimes worked well for me:

Occasionally I elect to present a very rough sketch of a proof on my slides--this allows me to show that the proof exists and give some sense of the tools required without getting mired in the intimate details of the argument or burying my audience in a hail of notation. Depending on how time is running I can either breeze through this sketch quickly or more slowly fill in some of the details and intuition verbally (though I would highly recommend against attempting to present a full proof in this way). In addition, I can also mention that I would be happy to provide the full proof to anyone who would like to see it.

Keep the slides with the proofs visible and explain -- upon reaching the first proof -- that you've included proofs for those that like to read ahead and you won't have time to go through them/all of them.

Response to DVSA:

That's terrible advice imo...there shouldn't be anything on the slides you aren't talking about...skipping the proof [looks] unprepared...

For every speaker there exists an audience member that is unengaged, because they've already understood the material. That audience member can engage themselves with the proof. By explaining, "I'll explain the general idea of the theorem; the proofs are included for those that like to read such details," your criticisms don't apply. This strategy will be appreciated by some often neglected members of the audience.

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    That's terrible advice imo. First of all, there shouldn't be anything on the slides you aren't talking about. Why would you put it there in the first place? Secondly, skipping the proof does look unprepared, you should know how long your presentation takes. The point of "I put it in so people can read it" doesn't make any sense either, because you skip it. So this only works if there are handouts and the proof can be attached at the end. In fact, it should be attached at the end, otherwise, people will start reading the thing you aren't talking about and no one is listening to the talk. – DSVA Sep 17 at 17:59
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    @DVSA It's excellent imo. (Can we please keep comments -- not just here, throughout this site -- positive?) I'll respond above. – user2768 Sep 18 at 6:50
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    I don't see how it's excellent advice to turn attention away from your presentation, even if you aim at a small group. Chances are you are turning attention away from other people too. This goes against everything a good presentation is about. And If you do it well a presentation can be entertaining even if you already know and understand the content. Preparing a talk for only a part of the audience and trying to engage the other part using some additional material at the same time is just a terrible idea. – DSVA Sep 18 at 7:56
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    @DSVA You're assuming this approach will "turn attention away from [a] presentation," I contend it will draw attention to the presentation by engaging more of the audience. (Again, please be constructive. E.g., rather than saying "[go] against everything a good presentation is about" -- which is false, since it cannot go against everything -- say what it does go against.) – user2768 Sep 18 at 8:28
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    I might(!) consider this approach if I knew the audience was very starkly split between beginners and experts, or if the presentation was mostly meant to be viewed as a recoding, but otherwise I think it's a huge "risk" for very little gain, as DVSA argues above. If you've got an example of someone successfully pulling this off though, I'd love to see a youtube clip or something. – Matt Sep 19 at 16:41

Don't ever say during your presentation, "because we're short on time, we're going to skip these next slides". That just highlights your failure to prepare a talk that is of the appropriate length, and annoys the audience by teasing them with content that they will not get a chance to see.

If you must prepare some extra slides, either because you don't know in advance how much time you will get, or how many questions the audience will ask, or how interested the audience will be in the technical details, then do it as professionally and seamlessly as possible.

One way is to use Keynote, in which case you can use an iPhone as a remote to control the slides. The iPhone will display a thumbnail of each slide, which lets you select the slide you want to advance to, and the audience will never know that you skipped anything.

Alternatively, set up the computer such that the external display is not a mirror of the laptop's screen. That could also let you select the slide from your computer without letting the audience see your supplementary materials.

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    I, for one, don't think it's annoying to see that there is more material that the speaker can fit in the allotted time. If I really am interested, I can ask them for their slides after the talk. And I don't usually hear other academics complain about it. – Federico Poloni Sep 19 at 18:21

Depends on the size of the audience and/or your ability to “read” them. You figure out in advance what to minimize if you sense they are following well or even bored; and what additional detail to go into if you sense they need it.

The most frequent reason I see for speakers skipping slides is that they were interrupted by questions and were suddenly under time pressure.

Of course, one can naively say "don't accept questions". Stuff happens. If an interviewee for a slot refuses to take an important question, that's it for the candidate, and they may as well stop. You may have a poor session chair that loses control. Again, stuff happens. If you insist, under such cases, to stick rigorously to your stack, you're being rude to other in the session, or you look unaware of the situation.

The best speakers need to be able to think on their feet.

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    Additionally, one of the most common reasons I've seen for getting questions is a presenter trying to gloss too quickly over a slide. – Karl Bielefeldt Sep 19 at 16:15

As an addition to the existing answers, if there are slides that you visibly skip over, you should explain why you're doing that. From personal experience, if the audience thinks you're trying to hide something, the whole atmosphere of the presentation can become antagonistic.

Some softwares have been suggested to help you skip slides without the audience noticing. I have two options for you in this regard, one is https://prezi.com/ which I have used a fair bit. It allows you to move in any direction between your 'slides' and the other, assuming you are working in PP, is to use 'action' buttons as links to other locations in your presentation (under links tab).

The drawback with both is that you need a thorough knowledge of your presentation, inside, out, back and forwards, as this is how you will be able to move through it!

Some people have complained that the transitions in prezi, very forwards/backwards and fluid, leave them feeling a little sea sick from watching.

Overall, its not a problem to skip slides as long as you cover all the evidence in different ways, such as talking ad-lib with another slide if its appropriate. There is no point in making people suffer the same information twice as that leads to the well known phenomenon of 'death by powerpoint'...

I wouldn't do this in a professional business environment, but for academia it's no big deal to skip slides.

For a seminar talk you will probably have differently formatted handouts, but in any other case it's common to hand out the slides and so they should be linear structured, not 2d or having half of the content in the appendix.

Sure you could try to estimate exactly what you will be able to present in the timeframe, but actually you can't. Your audience should learn something and so they should ask questions if they don't understand something. And based on how many questions there are you will not get anywhere near what you estimated.

I think the ability to adapt your talk to the audience to enable them to get the most out of your talk is far more important than to have a smooth, perfectly planned out show. On the other hand it's more likely that nobody asks questions, only very few can follow up to the last slide, but everybody sits there quite and politely. But that's not how it should be.

The difference to business scenarios is, that it's far more involving for the audience to understand proofs, than to grasp some facts about products and bar charts. And your not trying to sell anything so you don't have to keep a polished facade that might deteriorate by skipping around your slides.

  • That's curious. I don't think I've ever seen handouts for a seminar... In which fields does this happen in your experience? – Anyon Sep 18 at 11:39
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    @Anyon Computer science is my field of experience. Also includes a lot of proofs – daign Sep 18 at 15:24
  • I strongly disagree that this is okay in academia and even more vehemently disagree that you can't reliably make a presentation that fits in a designated timeframe (for any field). You can, of course, gloss over details to make up time, or go into more detail if you're somehow running way ahead, but both should be as seamless as possible, which mashing the right arrow while saying "And we don't have time for that" is not. – Matt Sep 18 at 16:31
  • @daign I see, thanks. It makes sense to do it for proofs, I suppose. Also, "see the paper for details" might not work as well in a field with mostly short conference papers. – Anyon Sep 19 at 0:43

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