Ines Pisetta - October 27th, 2020

This blog post aims to give a broad overview over the development of Commonsense Reasoning (CR) in the field of Natural Language Processing (NLP) and its multimodal intersection with Computer Vision (CV). What makes CR so important in the age of Deep Learning, how did the approaches to it and datasets for it change over time, what are the main challenges, how can other modalities than language contribute towards CR in Machine Learning and why is Commonsense Reasoning still a hot topic?

What is Commonsense Reasoning?

Commonsense Reasoning requires a machine to reason based on ‘knowledge about the everyday world’1 . This knowledge is assumed to be widely known by humans and so they most of the time omit any mention of it from text, visuals or other modalities.2
Examples for commonsense knowledge are abundant: A lemon is sour, in a waterfall, water flows downwards due to gravity, if you see a red traffic light, you are supposed to slow down and stop and you typically don’t make a salad out of a polyester shirt3 . Since all that knowledge is obvious for humans and thus rarely explicitly mentioned, it is hard to acquire for a machine, let alone reason with it.

This reasoning abilty based on commonsense knowledge is key to really understand a text and answer comprehension questions about it. CR is thus closely related to Reading Comprehension, Question Answering and Natural Language Understanding in general.

To perform Commonsense Reasoning, one has to consider facts about time, space, physics, biology, psychology, social interactions and many more.1 3 4

Why Commonsense Reasoning?

But why is Commonsense Reasoning a thing, anyway?
The question what makes a machine intelligent goes all the way back to 1950 when Alan Turing invented his famous Turing Test. In fact, Commonsense knowledge and reasoning is considered a vital part of machine intelligence5 and for machines to achieve human-level performance in various tasks, commonsense knowledge will most certainly be necessary3 .
The importance of real-world knowledge for NLP was first discussed in 1960 in the context of machine translation. 3 6
Since then there have been various approaches to the task of Commonsense Reasoning and to handling and acquiring commonsense knowledge, ranging from logic-based approaches over building handcrafted7 8 or crowd-sourced1 knowledge bases and web mining to more recent neural methods.3 9

How to test for commonsense?

Alongside the methods to tackle the problem there has always been the question of how to correctly evaluate Commonsense Reasoning. Over the years, several datasets have been developed for that purpose.

Winograd Schema Challenge

You most certainly have heard of the so called ‘Winograd schemas’10 . They have been developed by Levesque et al. in 2012 as an alternative to the Turing Test and are named after Terry Winograd (1972), who was the first to introduce them:

The city councilmen refused the demonstrators a permit because they [feared/advocated] violence.

A Winograd schema consists of a sentence, a binary question and two possible answers. Every schema involves two parties, a pronoun or possessive adjective in possible reference to both of the parties and the possible answers, which can be any of the two parties:

The trophy doesn’t fit in the brown suitcase because it’s too big.
What is too big?
Answer 0: the trophy
Answer 1: the suitcase

Key to a schema is the so called ‘special word’, that appears in the sentence and possibly the question. If replaced with its ‘alternate word’, the answer to the question changes. In the above example this special word is ‘big’. If we replace ‘big’ with ‘small’, the answer to the question changes from ‘the trophy’ to ‘the suitcase’.
Because of this special property, the schemas were said to be impervious to ‘tricks involving word order or other features of words or groups of words’10 .

Kocijan et al. (2020)9 provides a comprehensive overview over all variations of the Winograd schema dataset and over a broad range of approaches tackling the WSC, ranging from feature-based methods [1] (which are the oldest and still present), to neural ones without pre-trained language models [2] (2017 and 2018 mostly) and with the use of large-scale pre-trained language models [3] (starting in 2018 and still ongoing). An overview regarding the different performances of some of those models is provided in the table below. All results are achieved on a basic version of the Winograd dataset (WSC273) and values are taken from Kocijan et al. (2020) unless stated otherwise.

Model Accuracy (%)
Humans (Sakaguchi et al. (2019)) 96.5
Sakaguchi et al. (2019) [3] 90.1
Wang et al. (2019) [2] (unsupervised) 62.4
Liu et al. (2017) [2] (supervised) 52.8
Emami et al. (2018) [1] 57.1
Random guess 50.0

We can see that all approaches not using large pre-trained language models are far away from reaching human performance and closer to a random guess baseline. Unsupervised approaches using neural models [2] beat supervised approaches of the same category but are still far from perfect.
Neural approaches using pre-trained language models [3] though are really close to human performance with the best performing approach shown in the table (Sakaguchi et al. 2019).
However, systems that have succeeded on WSC273, didn’t show the ability to solve other Natural Language Understanding tasks like Commonsense Reasoning.9 They even aren’t able to answer simple questions about narrative text11, thus relativizing the high performance of language model approaches and the usefullness of the Winograd schemas as a benchmark for machine intelligence or a machine’s ability to perform Commonsense Reasoning.

Luckily, over the years several other benchmarks to test CR have been developed. Most of these are in fact crowd-sourced, which is reasonable given that Commonsense Knowledge is something inherently known by humans.

Other benchmarks

Not a benchmark itself, but a resource several datasets or approaches are built upon, there’s ConceptNet1 .
ConceptNet (2004) consists of a wide range of (commonsense) concepts and their relations as illustrated below:

Image from Liu and Singh (2004)1 : The structure of ConceptNet.

Story Cloze Test/ROC Stories (2016)12 : Based on a four-sentence context a system has to choose between a right and a wrong ending.

Image from Mostafazadeh et al. (2016)12 : Three examples for the Story Cloze Test.

SWAG (2018)13 : A multiple choice Question Answering dataset, derived from video captions. The goal is to predict which event is most likely to happen next. Also proposing a new method to construct a non-biased dataset (‘Adverarial Filtering’).

Image from Zellers et al. (2018a)13 : Examples from the SWAG dataset, the correct answers are highlighted in bold.

CommonsenseQA (2019)14 : Built upon ConceptNet a system has to answer a question that includes a specific source concept by choosing from five possible answers. There’s also a very competetive leaderboard for the dataset.

Image from Talmor et al. (2019)14 : a) source concept (green) and target concepts (blue) sampled from ConceptNet; b) workers generate three questions, each with another target concept as the right answer, additionally they provide two distractors: one chosen from ConceptNet (red) and one written by themselves (purple).

DROP (2019)15 is a Reading Comprehension benchmark that requires Discrete Reasoning Over Paragraphs. Based on a paragraph, a system has to answer a question that requires a comprehensive understanding of the paragraph. Types of reasoning include: subtraction, comparison, selection, addition, count and sort, coreference resolution, other arithmetics, set of spans and other.

Image from Dua et al. (2019)15 : Example from the dataset requiring subtraction to be performed; relevant parts of the paragraph are highlighted.

Explain Yourself!/CoS-E (2019)16 : Provided with a question, three choices and an explanation from the Common Sense Explanations (CoS-E) dataset, a system has to generate a valid explanation instead of chosing from the provided possible answers.

Image from Rajani et al. (2019)16 : Examples from the CoS-E dataset.

CODAH (2019)17 : This datasets consists of prompts, subjects and candidate completions collected specifically to target weaknesses of state-of-the-art neural question answering systems. Tested categories include idioms, negation, polysemy, reference and quantitative reasoning. This dataset is a more difficult extension to SWAG (Zellers et al. 2018a)13 .

Example (taken from Chen et al. (2019)17 ):
A man on his first date wanted to break the ice. He

  • drank all of his water.
  • threw the ice at the wall.
  • looked at the menu.
  • made a corny joke.

Event2Mind (2019)18 : A system is provided with an event (‘X drinks coffee in the morning’) and has to reason about the likely intents (‘X wants to stay awake’) and reactions (‘X feels alert’) of anyone who participates in the event.

Social IQA (2019)19 : The first large-scale benchmark for commonsense reasoning about social situations. Based on a given context, a system has to answer a multiple choice question.

Image from Sap et al. (2019)19 : Three triplets of context, question and possible answers, also mentioning the type of resoning that is required.

However, there are still more datasets available than mentioned here. Now we will take a closer look at the results that models have achieved on those benchmarks, why they might be problematic and why it is good to have several different tests for Commonsense Reasoning.

Recent approaches to CR and their problems

With the advent of the Transformer20 and the two most famous models built upon it, namely OpenAI’s GPT-121 and BERT22 , NLP as a whole experienced some drastic improvements. The area of Commonsense Reasoning also hasn’t been spared by those changes.

Up to 2018 the neural approaches in the field were trained mostly from scratch and still struggled heavily when attempting to perform Commonsense Reasoning.9 In 2018 the Transformer found it’s way into the field. Researchers started using huge pre-trained language models like BERT either with or without fine-tuning on their specific Commonsense Reasoning task and applied them to the available benchmarks – with huge success.

In fact, those models even outperformed humans on several tasks – a sign that there’s almost certainly something wrong. After all, our models are supposed to ‘think’ like humans or at least act like they would.
On critical examination it was soon obvious that the models didn’t really learn anything regarding commonsense. They didn’t perform well on other more sophisticated CR tasks, while having achieved high performance in tasks that were said to be good benchmarks for Commonsense Reasoning. The language models merely memorize and approximate world knowledge23 and don’t have a deep understanding of it yet.

An example of such a problematic case is shown in the table below.

Model Dataset Accuracy (%)
Human experts (Zellers et al. 2018a) SWAG 85.0
ESIM + ELMo (best from Zellers et al. 2018a) SWAG 59.2
BERT Large SWAG 86.3
BERT Large (trained on SWAG only) CODAH 42.1
GPT-1 (trained on SWAG only) CODAH 38.1
BERT Large (trained on SWAG and CODAH) CODAH 64.5
GPT-1 (trained on SWAG and CODAH) CODAH 65.3
BERT Large (trained on CODAH only) CODAH 28.4
GPT-1 (trained on CODAH only) CODAH 53.9

BERT surpasses the performance of human experts on SWAG, hinting it does not possess human-equivalent commonsense and rather exploits limitations of the dataset17 .
The results on CODAH, which is a more challenging extension of SWAG seem more sensible, irrespective of the particular training set.

If you are curious, how BERT and GPT perform on other datasets, here’s a quick summary of some results on other benchmarks presented before.

BERT achieves 55.9% accuracy on CommonsenseQA14 , while GPT reaches 45.5% accuracy. Both results are still relatively low in comparison with the human performance of 88.9%, possibly indicating a difficult dataset.

Rajani et al. (2019)16 test on CommonsenseQA v1.11 (which is said to be more challenging then the original CQA) while training on their own dataset CoS-E. They achieve 55.7% accuracy with their own CAGE-reasoning system compared to a BERT baseline of 56.7%. If provided with additional open-ended human explanations during training, BERT reaches an accuracy of 58.2% (CoS-E-open-ended). The authors also report performances on CQA v1.0.

For results on other benchmarks, please read the respective paper.
Now we’ll have a closer look at Commonsense Reasoning beyond Natural Language Processing.

CR in Computer Vision and Multimodality

Commonsense Reasoning has recently made it’s debut in the field of Multimodality, more explicitly in the joint application of both images and text.

Visual Commonsense Reasoning

Zellers et al. (2018b)24 introduced the task of Visual Commonsense Reasoning and constructed a dataset along with it. Their approach partly builds upon their prior paper that introduced the SWAG dataset (Zellers et al. 2018a)13 .

A model is provided with an image, a list of regions and a question. In a two-step Question Answering approach it has to choose the right answer for the question and a reasonable rationale to justify its answer.

Image from Zellers et al. (2018b)24 : Input to a system are the image with a list of regions and the question together with the answers. In a first step, the model chooses the right of four possible answers. In a second step, it provides chooses the most reasonable rationale among the four ones that are supplied.

To enable clean evaluation, the task is formulated as two-step multiple choice Question Answering approach Q -> AR. Each subtask consists of an image and:

  • a sequence of object detections
  • a query
  • a set of n responses

The first subtask is framed as Q -> A and the query consists of the question while the answers choices represent the set of n responses.
QA -> R is the reasoning subtask – in the end nothing more than another Question Answering task. This time, the query is made up of the question concatenated with the right answer. The responses are the provided rationales.

To collect questions, correct answers and correct rationales, the authors made use of crowd-sourcing while continously probing the quality of the data.
However, also retrieving the incorrect choice via crowd-sourcing was a) expensive and b) had the risk of annotation artifacts (subtle patterns injected unknowingly into the data by the workers).
Therefore, the authors made use of a technique called ‘Adversarial Matching’, where the incorrect answers or counterfactuals have to be as relevant as possible for the given query but at the same time not too similar to the correct response or rationale. An illustration of that can be seen below.

Image from Zellers et al. (2018b)24 : An overview of Adversarial Matching; incorrect reponses are obtained via maximum-weight bipartite matching.

For further details on the construction of the dataset e.g. regarding the selection of the images, details about the crowd-sourcing process or Adversarial Matching, please take a look at the paper.

Next we’ll take a look at the performance of several models on the dataset. Zellers et al. have provided a leaderboard on their website along with their first experiments in November 2018.
Within a year several other models entered the leaderboard and quickly had beated the original model of Zellers et al. The table below shows a comparison of the performance of selected leaderboard entries (accuracy %):

Model Q -> A QA -> R Q -> AR
Humans 91.0 93.0 85.0
UNITER-large* 79.8 83.4 66.8
ViLBERT* 76.4 78.0 59.8
VL-BERT 75.8 78.4 59.7
Unicoder-VL* 76.0 77.1 58.6
R2C 65.1 67.3 44.0

The value for human performance was provided by Zellers et al. (2018b) along with the dataset and their experiments. R2C is their original model which was soon surpassed by several other models, all of them making use of language models and most of them using ensembling (marked with *). If you are interested in a particular approach, please read the respective paper.

As we have already seen in Commonsense Reasoning for NLP, language models run the risk of exploiting limitations of datasets and not really learning commonsense. With the quick success of several such models in the field of Multimodality and considering this weakness, one has to scrutinize the performance of every model that attempts Commonsense Reasoning – be it in NLP, CV or in the union of both.

Ongoing research and your part in it

While we have observed a huge improvement in performance of Commonsense Reasoning systems with the advent of Transformer models in NLP and the field of Multimodality, research is far from over. Language models have been shown to exploit some of the available benchmarks while failing on others, making it obvious that those models currently don’t really have an understanding of commonsense.

Furthermore, there’s still reason to develop additional benchmarks to test the Commonsense Reasoning ability of systems. After all, the available benchmarks only require specific types of reasoning and by far not all that we see throughout natural language.

Besides that, there’s still an active branch of research dedicated to more ‘traditional methods’, mostly involving the incorporation of knowledge bases and logical representation into models.4 23 Especially for (but not limited to) reasoning about sciences like physics, these approaches are well-justified despite not being overly successful.

On top of that, there’s also ongoing research on Commonsense Reasoning in the field of Computer Vision and in multimodal approaches, incorporating NLP and CV. With the latter also recently making use of the Transformer and considering the problems of Transformers that have been shown in NLP, the question remains what our models really learn.

In addition to that, in the area of Commonsense Reasoning about videos like movies, research has barely scratched the surface. There have been attempts to provide basic Commonsense Reasoning video datasets25 , but we are far from reaching a deep understanding of media like movies, involving various kinds of reasoning. An example for that is the horsehead scene from the movie The Godfather, that involves several steps of reasoning.3

Image from Davis and Marcus (2015)3 : Each line shows one necessary step of reasoning.

If this blog post ignited or fueled your interest for Commonsense Reasoning, there are several places to start out:
AllenAI has built a team named MOSAIC, that has provided the field with invaluable contributions like Visual Commonsense Reasoning24 , SWAG13 , Event2Mind18 , WinoGrande26 and many more.27
Also, there has been the attempt to cover progress in NLP in form of a Github repository created by Sebastian Ruder. It has a section dedicated to CR, covering some systems’ performances on several CR benchmarks.
But most of all, one should keep an eye on all those papers that are published continously in the field. Hopefully this post gave you a good idea where to start for that matter.

Commonsense Reasoning is a very interesting and challenging area of research. It will be exciting to see what the future of the field will look like and if it will bring machines closer to human reasoning and behaviour.

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